Last update: March 15, 2024

How to Raise & Lower KH (Carbonate Hardness) in Aquarium & What is KH

Next up in our beginner’s guide to water chemistry is KH.

With KH’s ability to directly impact the pH of your tank, you’ll want to watch it darn closely.

Today, I’m going to teach you everything you need to know about KH.

But first, ensure you have these gadgets to effectively monitor you aquariums water quality:

What is aquarium KH?

Carbonate hardness is referred to as KH for short. It’s basically a measure of carbonates (CO3) and bicarbonates (HCO3) dissolved in your water.

Don’t worry! You don’t need to remember those words. You just need to know what KH is and why it’s important. And, that is actually simple…

Think of KH as a protective barrier that surrounds your pH. As your aquarium creates acids, they eat away at KH instead of affecting your pH

However, this barrier is not permanent and once gone, your pH is free to move around again.

The higher the KH of your aquarium, the more acid it can neutralize before the pH is affected.

KH is invisible. While it exists in your water, you won’t be able to know how much is there without a special test kit.

You might also hear KH referred to as the alkalinity of the water.

Important: Don’t confuse alkalinity with alkaline.

  • Alkaline: The opposite end of the pH scale to acidic (also referred to as basic).
  • Alkalinity: The measure of acid neutralization (KH).

And just to confuse you more, you may also hear KH referred to as the following…

  • Carbonate hardness
  • Temporary hardness
  • Total alkalinity
  • Buffering capacity/buffer
  • Acid-neutralizing capacity (ANC)

These can all be used interchangeably. So, if they ever come up in conversation, remember that they all refer to the same thing:


FishLab Fact: Carbonate Hardness is shortened to KH because it is derived from the German spelling of the word, Karbonate Hardness.

What is the difference between KH and GH?

Man comparing aquarium GH to aquarium KH

Beginners often confuse carbonate hardness (KH) with general hardness (GH). While both have the word hardness in their name, they measure different parameters of your water.

Carbonate hardness (KH): The measure of carbonates and bicarbonates dissolved in water.

General hardness (GH): The measure of magnesium and calcium dissolved in water.

If you have ever heard someone say…

I have really hard water where I live.

They are talking about GH.

In nature, GH and KH go hand in hand. If a waterway has a high GH, it will also have a high KH.

But tap water is usually anything but natural…

It’s actually possible for your tap water to have a really high GH and a very low KH. So, just having a high GH does not automatically mean that you also have a high KH.

Why is KH important to your aquarium?

As I touched on earlier, KH prevents acids from causing your pH to swing.

Rapid changes in pH can shock and even kill your fish. So yeah, it’s something you want to avoid!

Now, here is what you might not be aware of:

Your aquarium constantly produces acids.

You know those beneficial bacteria that live in your filter, the ones you introduced when you cycled your tank? Well, they are to blame.

Waste breaking down into ammonia, nitrite and nitrate in aquarium diagram

You see, fish poop breaks down into ammonia. Beneficial bacteria that live in your filter turn the ammonia into nitrite and then finally into nitrate.

But here’s the thing…

Nitrite and nitrate are acidic!

And because they are constantly being produced, the pH of your aquarium will decrease over time.

If your KH (carbonate hardness) is low or non-existent, then nothing can neutralize these acids.

This leads to an unsafe drop in pH that can make the water toxic for fish and plants.

KH is the invisible superhero in your tank that stops this from happening. As you see, it’s important to maintain some level of KH in your tank, no matter what species you keep.

In saltwater tanks, KH serves a second purpose. Corals use carbonates to build their exoskeletons. If you are creating a reef tank, you’ll need to watch that KH!

FishLab Tip: Have you ever tried to lower the pH of your tank but noticed it didn’t change? KH (carbonate hardness) is preventing the change. You need to reduce your KH before you can adjust the pH.

What is the best KH level for your tank?

The ideal KH levels entirely depend on what you stock in your tank.

Let’s look at the suggested ranges for different types of aquariums. While the measurements can be listed as part per million (PPM), I prefer to use degrees of carbonate hardness (dKH).1 dKH is about equivalent to 17.9 ppm

Please note, the following recommendations are rough guidelines only. Your specific fish, plants or invertebrates may require more precise KH levels outside these ranges.

Freshwater KH

Tropical Fish Tank4-8 dKH
Shrimp Tank2-5 dKH
African Cichlid Tank10-18 dKH
Discus3-8 dKH
Planted Tank 3-8 dKH
Brackish Tank10-18 dKH
Pond4-8 dKH

Saltwater KH

Saltwater Tank8-12 dKH
Reef Tank8-12 dKH

Will increasing my KH also raise my pH?


The two go hand in hand.

Generally, as KH rises so does pH. But don’t let this scare you away from maintaining a healthy KH.

Having a stable pH that is a little high is much better than a pH that swings up and down all the time.

How do you test the KH of your aquarium?

It’s important to know the KH level of your water.

Unfortunately, because KH is invisible, you’ll need a special aquarium test kit to do it…

Accurately measures GH & KH
API GH & KH TEST KIT Freshwater Aquarium Water Test Kit, 2.5 oz.
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Don’t worry! It’s affordable and easy-to-use. Best of all, a single KH test kit can last for hundreds of tests – just follow the instructions.

Note: The results of the test can be given in dKH or PPM. Which you use is a matter of choice. I personally use dKH and refer to it from now on.

While there are aquarium test strips available that can also test for carbonate hardness or KH, I don’t recommend them. Based on personal experience, test strips are much less accurate than liquid test kits.

You may be wondering…

How often should you test the KH of your aquarium water?

Well, it all depends on the results of your test kit.

For freshwater tanks

  • 4 dKH or lower: Check your KH weekly.
  • 5 dKH or higher: Check your KH monthly.

You should test not only your tank but also your tap water. This will give you a greater understanding of how to go about adjusting your KH if you need to.

For saltwater tanks

I recommend testing your KH weekly. You should also check the KH of your salt mix, just to make sure everything is as it should be.

How do you increase KH?

Tested your aquarium water and want to raise your KH?

Let’s take a closer look at how you can do exactly that.

1. Water changes

Man performing a water change on his planted aquarium with gravel vacuum used as siphon

Many water supplies across America have a KH high enough that performing a water change will replenish the KH levels in your freshwater tank.

Test your tap water and see if it is over 4 dKH. If so, a weekly 25% water change will replace the depleted KH.

Take this time to also maintain your tank. I highly recommend buying a good gravel cleaner and using it to suck all the gunk out of your substrate. Doing so will help prevent nitrates from building up and decreasing your KH.

As for saltwater tanks, a good salt mix should contain all the essential ingredients needed to restore the KH in your tank.

2. Alkalinity buffers

Many aquarium brands manufacture their own line of alkaline buffer products. Depending on the brand, they may rely on baking soda, soda ash or phosphate to increase KH.

So, why wouldn’t you use each of these individual products instead?

Well, the manufacturers of alkalinity buffers have spent a great deal of time ensuring consistency. These ingredients are mixed with other elements to ensure that you achieve your expected KH.

For beginners, I personally recommend using an alkalinity buffer over other methods in this list because it takes the guesswork out of adjusting your KH.

Best of all, there is an alkalinity buffer designed to match exactly what you stock in your aquarium…

Freshwater Tank Alkalinity Buffer

Alkaline Buffer, 300 g / 10.5 oz
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Marine Tank Alkalinity Buffer

Brightwell Aquatics Alkalin8.3-P - Alkaline KH Buffer Powder for All Marine and Reef Aquariums
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06/14/2024 03:09 am GMT

Reef Tank Alkalinity Buffer

Reef Carbonate, 2 L / 67.6 fl. oz.
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There are even alkalinity buffers designed for specific species of fish, including…

  • Goldfish buffer
  • Discus buffer
  • Malawi Victoria buffer
  • Tanganyika buffer
  • Arowana buffer

There really is an alkalinity buffer for everyone!

FishLab Tip: Avoid phosphate-based buffers. Phosphates can deplete essential minerals like calcium and magnesium from your aquarium. Also, high phosphate levels can help fuel algae outbreaks and stunt coral growth.

3. Crushed coral

Crushed coral used to raise KH in aquarium

Yep, this is exactly what it sounds like. Crushed coral comes from dead coral reefs. Because it is high in calcium carbonate, crushed coral can help boost your tank’s KH.

Crushed coral can either be mixed in with your substrate or placed in a media bag and added to your filter.

Best of all, you don’t need to add it to your tank constantly. You just let it sit there and do its thing.

Carib Sea ACS00150 Crushed Coral for Aquarium, 40-Pound
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How does it work?

Remember those acids I mentioned earlier in the guide?

Well, these acids react with the crushed coral, causing it to release calcium and carbonate into your water, raising both the KH and GH.

How much crushed coral should you use?

It doesn’t really matter. You see, adding more crushed coral will just cause it to increase the KH and GH faster.

However, given enough time, a small or large amount of crushed coral will eventually raise the KH and GH to the same point. Your water will equalize.

This is because as your pH rises, it becomes less acidic, and the coral won’t release as much calcium and carbonate.

I personally recommend adding crushed coral to your filter. If you add crushed coral to your gravel, it can compact over time, trapping fish waste, uneaten food and other gunk. If you do add it to your gravel, only use a small amount rather than laying down a thick layer.

4. Aragonite

Crushed Aragonite used to raise KH in aquarium

Aragonite is the crystal form of calcium carbonate (CaCO3). Just like with crushed coral, acids in the water cause aragonite to release calcium and carbonate.

However, unlike crushed coral, aragonite is made up of tiny sand-like grains. Because of this, it is often used as a substrate sand in both freshwater and saltwater aquariums.

Aragonite can greatly increase pH, GH and KH over time. So, it’s best suited to hard-water-loving fish like African cichlids.

I don’t recommend aragonite for beginners. If you decide it’s messing up your water parameters, you’ll have to remove the entire substrate – a frustrating job once your tank is set up.

5. Dolomite rock

Crushed dolomite used to raise KH in aquarium

Dolomite rock, sometimes called dolostone, is a calcareous rock made up mostly of calcium, magnesium and carbonate CaMg(CO3)2.

As you might expect, it will release all three of these elements into your aquarium, raising both the KH and GH of your tank.

Dolomite will release less of these ingredients at a higher pH. Because of this, dolomite is more commonly used in freshwater aquariums. The higher pH of saltwater tanks reduces the dolomite’s effectiveness.

Dolomite is available in a wide variety of colors, making it suitable to be used as a substrate.

6. Soda ash

Spooning soda ash out of a jar to raise KH in aquarium

Soda ash is sodium carbonate (Na2CO3). Because it can greatly increase pH, it is mostly used in saltwater tanks.

If you want to add soda ash to your tank, it’s best to add small daily doses rather than a larger weekly dose. This will give you a better opportunity to react to how it is affecting your pH.

How much soda ash should you use? Bulk Reef Supply has a great calculator that takes the guesswork out of dosing.

How do you decrease KH?

As I mentioned earlier, KH helps prevent your pH from dropping.

But what if the pH of your tank or tap water is too high for your fish or planted tank?

Well, to lower your pH, you first have to lower your KH.

And if your water has a naturally high KH, then you have to lower that before you have any success at reducing the pH.

While raising your KH is a simple task, lowering it is more difficult. A balance needs to be struck between KH and pH. Otherwise, you’ll experience pH swings that can kill your fish.

Decreasing KH is really only done in freshwater aquariums. Let’s take a closer look at the different ways to reduce the KH levels of your tank…

1. Acid buffers

Seachem Acid Buffer 300gram
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To put it simply, acid buffers convert KH to carbon dioxide (CO2). The result is a reduced KH and a lower pH.

My number one tip when using an acid buffer:

Go slow!

Acid buffers are primarily used in planted tanks where the plants remove the extra carbon dioxide from the water.

However, if you don’t have plants, overdosing can result in both excess CO2 and a plummeting pH.

And, the end result is a bunch of dead fish.

So again, follow the instructions and take your time. You can always add more later.

2. Distilled water

Bottles of distilled water

Distilled water is water that has undergone a special process to make it pure…

The water is heated until it turns to steam, it is then passed through a cooler and collected in a separate container. All the impurities are left behind. The result is nearly pure water – no KH.

You can find it on the shelf of your local grocery store in gallon jugs.

Now, you want to mix this water with your tap water as you still want some KH and GH.

But by mixing it with say 50% tap water, it will adjust the KH accordingly. Use your aquarium test kit to determine the correct ratio.

The downside is the cost. Even though distilled water is fairly cheap per gallon, the costs can soon add up. Weekly water changes on a large tank can require a surprising amount of water.

For this reason, distilled water is best used for smaller tanks.

If you have a larger-sized aquarium, then my next solution is more appropriate.

3. RO/DI water

RODI unit to create pure water for aquariums

Make your own pure water with one of the following units:

  • Reverse Osmosis (RO) System
  • Deionization (DI) Filter

Both of these devices can be used to create “pure water” with no KH.

While the set-up costs may be pricey, it will save you a considerable amount of money in the long term, especially if you buy bottles of distilled water each week.

Just like distilled water, you want to mix RO/DI water with your tap water to ensure there is at least some KH and GH. The RO/DI water will reduce your KH proportionately to how much you mix in.

If you have a saltwater tank, it’s basically expected that you will have one of these units nearby.

4. Indian almond leaf

A pile of dried indian almond leaves ready for aquarium use

Indian almond leaf is a favorite for lowering the KH and pH of freshwater tanks. It’s particularly popular in betta tanks.

As the Indian almond leaves break down in your tank, they release tannic acid (tannins). These tannins eat away at the KH.

Indian almond leaves may also have medicinal properties, naturally protecting betta from skin issues and helping wounds heal.

For more information, check out FishLab’s detailed Indian almond leaf guide.

The downside to Indian almond leaves is that they gently lower the KH and pH of your aquarium water. If your water has a significantly high KH, you might not notice much of a difference.

5. Peat moss

Two hands holding peat moss used to lower KH in aquariums

Peat is dried and chopped peat moss. Put it in a mesh bag and place it inside your filter.

Like Indian almond leaves, peat leaches tannic acid (tannins) into the water to reduce the KH and pH a bit. Again, it’s best used where only a small reduction in KH is needed.

If you want to use peat to lower your KH, buy an aquarium-safe variety. Many types of peat are sold for use in gardening and are mixed with chemicals to cut down on mold, which could kill your fish.

Why should your KH levels NEVER reach zero?

For freshwater aquariums, you might have come across advice to lower your KH (carbonate hardness) to zero.

A KH of zero is particularly dangerous because it can lead to unsafe drops in pH that makes the tank toxic to both fish and plants.

Ideally, you want to maintain at least some level of KH in your tank, no matter what type of species you keep.

I most commonly come across this advice for fish like discus or certain types of shrimp. And yes, it’s true there are plenty of fish that live in a natural environment where the water has a KH very close to zero.

But here’s the thing. Those waterways have a LOT of other variables that help keep the pH level relatively stable.

No matter how hard you try, you cannot consistently replicate that environment in something as small as your aquarium.

Unless you are an expert fish keeper, I highly recommend that your aquarium has some degree of KH.

Fish need a stable pH for long and healthy lives. KH helps you achieve just that.


For beginners, KH or carbonate hardness is one of the most overlooked and least understood elements of aquarium chemistry. And, I can’t help but feel that API not including a KH test in their master test kit is part of the reason.

But never fear because now you know everything there is to know about it.

As you see, KH plays a vital role in keeping your water parameters stable.

Without it, your pH would bounce all over the place, stressing your fish and causing all kinds of problems.

And if you want to adjust your pH, then you need to change your KH first.

Do you test your tank’s KH levels? Let me know in the comments below! Also, don’t forget to check out these products for a optimal fishkeeping experience

Ian Sterling

Ian Sterling, founder of, began his aquarium journey over 30 years ago, driven by a deep fascination for fish and their diverse personalities. His website,, is dedicated to making fishkeeping accessible and enjoyable, offering beginner-friendly guidance, expert insights, and a community for aquarists to connect and share experiences.

Comments (144)

I have a new 55 gallon Mbuna tank and have been testing the KH and GH routinely. The tank has been established about one month. I have crushed coral substrate. The KH runs between 6-8 with it most often at 7. The GH runs 10-12 with it most often at 11. I do have Seachem Cichlid salt and Malawi buffer and have used both twice, using 1.5 tsp each, to try and raise the KH slightly to the recommended level. I did not see and appreciable difference. My pH is consistent at 8.0 and am nervous to raise the pH too much. What would you suggest I do to raise the KH? How much Cichlid salt and Malawi buffer can I use to safely raise the KH? Thanks for your help!

Hi Sharon,

To start with you add the Malawi buffer each day until your KH is where you want it. Malawi/Victoria Buffer is formulated to maintain the pH between 7.8 and 8.4 – which should be just fine for your Mbuna tank.

From memory, the instructions on the KH buffer are something like one teaspoon per 20 or so gallons, so 1.5 teaspoons probably isn’t enough for your tank size. Double check the directions for the correct dosage.

Just keep dosing each day until you reach your desired KH. From here, it’s maintenance dosing, such as when you do a water change or every 2 or so weeks.

Helllo Mr. Sterling. My ph has dropped to 6 so I’m planning on using an alkalinity buffer. Does this buffer also increase ph and do I add more weekly to maintain that ph/kh? Thanks!

Hi Ben,

Alkaline buffer will also raise the pH of your aquarium. How often you add it, will entirely depend on the rate at which your pH and KH drop. You’ll need to monitor with an aquarium test kit in order to determine your dosing schedule. I would add that before using an alkalinity buffer, I would try to determine the cause of the drop – if the cause is fixible, you may not need to buffer your KH at all.

Thanks for the help, I got my kh and gh test kit today. My kh is reading 4 dkh. Is that too low or too high. I expected it to be much lower because of the ph drops I have been experiencing. Also, is the general hardness of the water a big deal? Currently, I am cycling my tank and my ph has dropped to 6. I have no fish in the tank or plants. My cycle has seemed to stall since my ammonia are no longer converting to nitrite. My alkalinity buffer is coming tommorow ????. Is this a huge cause for concern? Will my bb die? Thanks again- Ben

4 dKH should be more than enough to buffer water – it’s the minimum that is often recommended for tanks and should be more than enough to stop your pH levels from bouncing.

There are studies that indicate nitrosomas and Nitrobacter (beneficial bacteria) won’t grow at levels below 6.5 – the water becomes too acidic for them. It is possible, but not guaranteed that your existing bacteria will die off, if they have grown at all.

I have some questions:

What is the pH of your tap water?
What is the pH ammonia, nitrite and nitrate content of your aquarium water (in ppm)?
What else do you have inside your tank?
How long have you been cycling for?
Are you performing water changes?

Something must be responsible for this dip, we need to get to the bottom of this or you’ll have problems long after cycling is finished.

My tap water ph is 7.6 the ammonia in my tank right now is 4ppm (I added some to my tank to feed my bb a few days ago not knowing my ph was low), nitrites are 0 and nitrates are 5ppm. All I have in my tank is aquarium safe substrate, a fake plastic plant and a betta leaf. I have a HOB filter. I have been cycling for about 2 and a half months now. I have added baking soda in the past to raise my ph. My ph has dropped a few times like this before. If my bacteria dies will it be due to no food since the ammonia is ammonium or because of the acidic water? Does this mean I have to restart my cycle? Thanks again- Ben

Hi Ben,

It’s the acidity that will kill off your beneficial bacteria, at a pH of 6 this is the potential reason why your cycle has stalled. It’s less about restarting your cycle and more about extending your cycle process.

If your ammonia is not decreasing daily, and your nitrates increasing, then your tank is a long way off being cycled. Is your ammonia dropping at all over the days?

Two and a half months is certainly on the longer end of cycling, to the point where I would be concerned why it isn’t happening quicker.

Are you adding dechlorinator, such as seachem prime to your tap water prior to adding it to your tank? A drop from 7.6 to 6 is quite large, and you’ll need to figure out what is causing it. What substrate exactly are you using? I’m trying to narrow down all the possible causes…

For a comparison, what happens if you place your dechlorinated tap water in a class and leave it alone for a few days, does it also drop? If not, then something in your tank is responsible.

My ammonia used to decrease to 0 after a full dosage in one day but it seems my cycle has stalled. My ammonia is barely moving since the drop. I don’t want to add baking soda and my alkaline buffer hasn’t arrived yet so I’m stuck. I do use API tap water conditioner. My substrate is top fin gravel. I will retake the kh test today because there is a possibility I tested wrong. I will put some conditioned tap water in a glass and test it’s ph over the next few days. Thanks for all the help- Ben

The good news is that if the tap water doesn’t decrease in pH, then you won’t need a KH buffer. You can just keep doing water changes to keep the pH constant. On that note, have you done any water changes over the two and a half months you have been cycling? Other than the recent one?

I have done water changes… about five. One of them was to lower the ammonia level because I dosed up too high. The rest were an attempt to raise my ph since it dropped. The water changes couldnt seem to get my ph over 6.8… The ph ended up dropping even after the water changes. I got frustrated and added baking soda which kept my ph constant for a good three weeks. My ph buff has come in the mail today, should I use that in an attempt to save my remaining bacteria or should I do a water change? -Ben

The water changes didn’t seem to help so far, right? A buffer should increase your KH to above 4, which is the KH of your tap water, which should help with the pH drops. Admittedly you could do both of you wanted, But the big focus needs to be what is causing the pH drops. Otherwise you will be having this problem forever.

I’d follow the instructions,re-test and monitor what is happening while you hunt for the cause.

Thanks Ian, I added the alkaline buffer to my tank but for future purposes how would I use the alkaline buffer without killing my fish from the drastic rise? I will keep you posted on the conditioned tap waters ph levels over the next week.

It’s a balancing act since the buffer should improve your pH levels as well. Depending on the buffer you purchased, follow the directions. Alkalinity buffers are tested at their dosages so as not to nuke your tank.

For instance, here is Seachems directions:

Modify the routine as per your tank and tests.

Good news Mr. Sterling, my bb survived! Yesterday I added the Alkalinity buff (sea chem) which brought my ph up to 7.6. I still had 4.0ppm ammonia. Today my ammonia is testing zero with a 7.6 ph. I retested my kh after adding the buff and it was 5dkh. Thanks for all the help, Ben

Update: the conditioned water sitting in a plastic container has remained constant at 7.6 ph. My aquarium however has dropped again to 6ph. The kh is 4dkh. I guess it is something in my tank causing these drops. What could it be? The substrate possibly or maybe the plant? I really don’t want to have to clean out the whole tank and start from scratch. The weird thing is I have never experienced these ph drops until my cycle had started. Anyways, I added some alkalinity buff to my tank to raise the ph. Thanks- Ben

Hi Ben,

That’s why I tried to stress earlier that something in your tank is responsible for the drops and any measures you add to your tank will not solve the problem long term. It’s going to be a trial and error approach. You can either remove one thing at a time, or all at once. I’d personally do it bit by bit, so at least you know what’s causing the issue in the future and how to avoid it.

How is the water doing that you left to sit, has the pH of that dropped or is it the same?

The ph of the water in a separate container is remaining constant so I guess it is something in the tank. Will removing things from the tank affect the bb population or not make much of a difference because most live in the filter. Thankyou.

The good news is that because the majority of beneficial bacteria live in your tank, removing other things shouldn’t make any difference. It’s one of the major advantages of using a filter.

Hi Mr Sterling
Thank u for your great guides and valuable experiences.
As I was novice in running my saltwater tank, I used dead corals instead of live rocks in my tank and after about 5 months my KH is pretty off the chart, about 13000 ppm.I have removed the dead corals and I changed 20 percent (80 L) of the tank and decreased it to 9000 ppm. If I change 180 L again, it will get under 500 ppm. will it be harmful for tank inhabitants?

Hi Alireza,

Unfortunately, at this point in time, my site only focuses on freshwater tanks. I would suggest asking at a forum, like “reef2reef” or “reefcentral”

Who knew keeping goldfish could be so difficult! Next time someone offers free fish, I think I’ll politely decline. The problem is that I am attached to these things now more than the kids are.
Just before Christmas we got a brand new 30 gallon tank with filter, protein skimmer etc. Only have Walmart decorations and gravel.
There are 9 baby goldfish – just plain not fancy – about 1″ to 2″ in sizes, they don’t have their colors yet, but one is starting to get a black racing stripe on top which I was afraid was a result of high ammonia.
I cannot seem to get the ammonia down. I do regular water changes of about 10% of the tank. I got a gravel vac and have used it twice in the past 2 weeks. We have a whole home soft water system, so any tap water I add sits out for 24 hrs before the change.
I used Tetra strips to measure ph and fluval chem test to measure ammonia.
Tap water results don’t change after 24 hrs. nitrite/nitrate 0, GH ppm about 50, KH ppm 300, pH between 7.8 and 8.4, results are very similar with aquarium water.
Fluval chem test shows results between 2.4 and 3.7 for ammonia.
How do I get it down?? The fish seem to be in okay health, but did notice them going to the surface more and one day 2 wks ago where they were darting around the tank on super speed. That’s when I did the gravel vac and a 20% change. added an ‘ammonia’ filter and changed the big carbon filter. Still no change in numbers. Really don’t want to kill these little guys off.
Any advice is greatly appreciated!

Oh, this must be a huge shock. Fish are one of the more difficult fish to keep, as you don’t just have to worry about the health and well being of your fish, but it’s environment too. The environment is the hardest part.

9 goldfish in a 30 gallon? This is going to be difficult. Generally speaking, it’s 20 gallons for a single plain goldfish and an extra 10g for every additional. These fish have a high bioload which leads to them pooping and peeing more, which leads to their tank gunking up quickly. This is very likely the reason for the high ammonia. As this waste all breaks down, it releases ammonia. You’ll forever have water quality issues with this many goldfish in a tank of this size a weekly water change of 10% won’t cut it. You’ll need to do closer to 50% regularly, maybe even daily. You use your test to determine how often to do this, but once a tank has cycled, the ideal ammonia is zero. Ammonia filters just hide the problem and once they are used up, need to be replaced. It locks you into a constant cycle of buying new ammonia filters.

The goal should be to cycle your aquarium. This process allows beneficial bacteria to grow in your tank that help break down the ammonia on their own. I have a fish-in cycle guide that breaks all this down into easy to understand chunks.

Even so, you will forever have problems with this many goldfish in a tank of that size.

Thank you so much for all the guidance. After reading around, I realized they would be fairly labor intensive with water changes. I don’t mind this part, I just want to keep them healthy.
I have been doing about a 50% water change every other day since my original post, but after reading your reply and the fish-in cycle, I realized I don’t think any of the bacteria are growing. I have not been using a conditioner at all, and we have town water. I suspect our softener system doesn’t remove the chloramines.
I have purchased API Stress Coat and done a 50% water change today. At the moment, Ammonia is at 1.0 on the API Master Test, no nitrites or nitrates yet. I will check again tomorrow.
I also have a question about Ammonia Lock additive. Do I add it at the same time as the conditioner? How will this affect my test results?
Thanks again for your help!

Hi Julie,

If your water does in fact contain chlorine or chloramine, then it’s impossible for beneficial bacteria to establish themselves. If this is the case, then you are at the very start of the cycle and it could take a week or two before nitrites start to appear.

Unfortunately, I cannot help you on the ammo lock, while I suspect you can add it at the same time, I cannot guarantee this. I personally use seachem prime, which is an all-in-one conditioner for chlorine, ammonia, nitrites and nitrates.

Hi Julie,

You DEFINITELY need to add a water conditioner that neutralizes chlorine and chloramine.

Chlorine and chloramine are highly toxic to the beneficial bacteria colony that you are trying to establish and maintain.

I also recommend adding Seachem Prime to any new water that you put in the tank.

I would also recommend Seachem Stability and Seachem Pristine.

They are beneficial-bacteria-in-a-bottle.


After many painful tank water changes, I finally realized that I was adding the Stability and Pristine without first adding the Prime to my bucket.

I was killing the bottled bacteria with un-conditioned tap water (chlorine/chloramine).


Hi, I’ve just inherited a tropical fish tank. New to this, everything is good, except the carbonate hardness which is 15 dh. How do I correct this? Any advice would be appreciated, thanks Vicky

Really good guide…Quick question, I have started a planted aquarium with easy plants and before I go deeper into the rabbit hole I wanted to know if my KH is 6 and PH 8.0 degassed will this cause an issue growing plants.

Would I need to get RO / DI to lower my KH and in turn my PH.

Hi Paul,

It entirely depends on what plants you are growing and their preferred parameters. RO/DI water will indeed lower both.

Hi Ian,

I use bottled water for my 25lt nano aquarium, however, our water here has high pH & KH.
I saw 2 products out of 100’s 🙂

1. Seachem Neutral regulator claiming that it will adjust pH to neutral 7.0 from either a low or high ph, plus it also removes chlorine, chloramine or/and ammonia. however, there is no info about lowering KH which is also important for me. But lowering ph will also lower kh is that correct ?

2. Seachem Acid buffer which is also on your list.

option one looks more user friendly since i want to have pH 7.0

I really appreciate your help on this.


Hi Mert,

Your thoughts are correct here, lowering pH will also lower the KH. I have no experience with Seachem Neutral Regulator, however, reading your description, it sounds like an interesting If it can do all that, then it sounds like the easier option to get your pH to 7 then go about increasing KH from there?

Both are viable options, if you have fish inside your tank already, make sure that the adjustment process is slooooow. pH shock is real.

Thanks Ian,

I have one more thing to ask,
Ph 6.8
Kh 5/6
Gh <3
This is my tank today… with no additives, maybe because of Co2?
I decided to move on with RO water, as of today (will add seachem equliblirium ) but ro has very low ph/kh. I am a bit worried changing 30% water with even lower ph.

What do you suggest ?

Thank you very much

Hi Mert,

I’m a little confused as to what you are asking here, everything sounds normal on your parameters. RO water changes will certainly soften the water, you’ll have to use an additive to raise the KH before doing the change otherwise there will be a dramatic drop.

Hi Ian,

You are right to be confused, since English is not my mother tongue, i might have done some mistakes in writing.

I used bottled water since i set my tank and it is stable, the water readings above is my “bottled water” readings. I found out that my aquarium shop is selling RO water and i decided to go ahead with it (not started yet but i have it at home) i read from your blog that i have to season it with seachem equlibrium since it is a fully planted tank. There are some other chemicals as well but i trust seachem.

My other problem was to keep my stable ph (6.8) stable 🙂 if i understand correct RO water has no ph/kh and doing 30% waterchange with RO water with only seachem equlibrium is good but not enough. I need to raise my RO water ph to 6.8 before adding it to the tank with some other chemicals or perhaps mixing RO with bottled water.

Another concern of mine is i have tested all the bottled waters i can buy including the tap water and the one i use (like the rest) has 8.0PH (which was one of the main reason i wanted to use RO) but somehow the tank has 6.8ph, i use C02, tropica plant soil, mopani wood and almond leaves, (a little low on GH but i will add some equlibrium today to raise it 5/6). My biggest fear is If this 6.8ph is something temporary i might have problems in the future.

It seems that either i will use RO water with equlibrium + some other checmicals “like a chemist” which will help to raise my gh/ph/kh to current level or i will continue using the bottled water and hope that it will somehow drops that 8.0 ph to 6.8 as it does since now.

Another question about the ph calculation;
Lets say if i have 20lt tank with 6.8 ph, if I do i waterchange (50%) with 8.0ph than the actual ph after the waterchange should be (6.8 + 8.0) / 2 = 7.4 is that a correct calculation or do mother nature might have other plans ?

Thank you for your patience 🙂

Kind regards

Hi Mert, not a problem, I wouldn’t have guessed english is your second language, you speak it better than me 🙂

I have an alternate solution, why don’t you use an acid buffer to lower the KH of your other sources? Seachem makes one. They also make a “natural regulator” that adjust’s pH to a constant 7. I know it’s .2 higher than you wanted, but it might make things easier if your fish can tolerate it, which they most likely can.

On your calculation, it’s sound in theory but also depends on the GH and KH of the water. It would be difficult to get it exact using this method.

I hope that helps and if you need any more clarification, please ask 🙂

Im using continuum reef basis kh buffer
I need to increase 7dkh up to 9dkh
5ml 1dkh … so can i drop 15ml per time ??

Hi Thana,

You would have to reach out to the brand directly. I have no experience with Continuum products.

Thank you for breaking this down. I’ve watched endless videos on YouTube and read articles and have been so confused….until now! I’m already feeling more confident in my newness of the hobby and ability to be successful.

Hi Aleesha,

It can be a bit daunting when you are starting out, but hang in there! It quickly gets easier. Wishing you all the best of luck!

Hi. I think I need help with my kh in my freshwater tanks. I’m on a well and my ph comes out at 4.8. But my kh takes 17 drops to turn yellow. I believe that’s 302. Fish seem healthy and my Cory’s and angels have been breeding well. What should I do?. I do have crushed coral in my filter and some aragonite in the substrate.

Hi Steve,

4.8 is far too low for most fish. To put it into comparison, that’s a similar pH to a cup of coffee. If your fish are still alive and seem healthy, I don’t believe your pH would be this low. What are you using to test? Most aquarium test kits don’t even go that low. I would double check with a different test to confirm? Most fishkeepers use the API pH aquarium test kit.

Hi Ian It would be great if you could advise us..We want to have a no maintenance pond (!) for plants and maybe wild life. The pond is about 6×4 ft and depth of 2-21/2 ft deep with a shelf at both ends. It was filled with tap water which had stood in a tank for 3 days. It turned green over 3 weeks and plants put in it for 2 weeks started to turn yellow and pale. Fish shop staff tested water and said put in 200 gm of KH- buffer up. We did and bought a KH test kit. KH read 18 drops. We did a partial water change, waited for 3 days and kh is now 13. We’re finding it confusing to know what it should be for our purposes and is this kh too high for plants and wild like. Mosquito larvae love it! Any help would be appreciated.

Hi Yasmin,

It entirely depends on what plants you want to add to your pond. If you search for the plant name + the word “Kh” or “dkh” it there should be a wide number of resources informing you of the plants preferred water quality.

Hi Ian…

If I use crushed coral in my canister filter, at which range will my KH stabilize…?

Would the answer depend upon the KH of my tap water?

I only ask, because some of the powder buffers state a specific number for KH, or a range of KH.

I have a fantail goldfish tank. I like the idea of keeping the KH and pH relatively stable, using crush coral in part of my filter.

Tanks, in advance!


Hi Dave,

Unfortunately, the answer here is “it depends” on the composition of crushed coral and a variety of other factors such as the rate at which acids are created in your tank. It’s one of the downsides of using a more “natural” means of balancing your KH, it’s more difficult to reach an exact KH.

Hi Ian,

Thanks for your reply.

I enjoy getting so much information from you!

I have ordered an API GH/KH test kit, and Nature’s Ocean Pacific Coral Gravel.

I don’t think my goldfish need an exact KH, but definitely a stable KH.

Thanks again, for all of your help.


Glad I could help, Dave!

I recommend testing your KH before you add the Crushed Coral – It’s possible that your tap water already has a high KH content. That’s the annoying thing about all this stuff, we can’t tell what’s happening inside our tank without a test kit. I’m sure you are all over it though!

Hi Ian,
Great post! Really cleared up the confusion of alkalinity for me. I have a 5 gallon freshwater tank. It was doing fine until my betta die while I was gone for the weekend. It got caught in the filter. Ever since my levels have been ridiculous. My ammonia was through the roof. I’ve been doing regular water changed to aid with lowering the ammonia. I bought a ton of live plants, but ever since my ammonia hasn’t left stress levels and my pH has been on the acidic side. I’m going crazy. Luckily my fish have been doing well, but I can’t keep any ghost shrimp. What am I doing wrong. I’ve practically replaced almost all the water out over time through changes but ammonia still is very present, KH is high and pH is low (acidic). I’m at my wit’s end. Please help!

Hi Dominique,

Did you crash the cycle in your tank by removing or replacing the filter? High levels of ammonia in an otherwise well kept tank may suggest that you need to re-cycle your tank.

Excellent explanation. 5 Stars.
My issue is:
5gal planted tank. Only 5 Endler’s in the tank, a few Otos, and I keep adding a few cherry shrimp every month or so. Everything was rock solid readings for the past six months or so.
But in the past few weeks, the PH has started to lower to below 7 and is now down to about 6.8. I’ve been doing water changes, checking TDS, ammonia, nitrate, changing filters…but it continues to slowly drop. The KH has been slowly dropping too and yesterday it was 2-3 drops on the reading. Too low! A couple of the older shrimp died a few days ago. I ordered a digital PH meter and some alkaline buffer (arrives tomorrow). Hopefully, this will raise the KH and the PH back to around 7.2

Hi Thomas,

5 gal is a very tiny tank, it always surprises people just how few fish they can fit inside a tank – it’s likely that your water issues are from overstocking, ottos especially need a larger tank. Remember, just because it can fit, doesn’t mean it’s a good idea. Your local fish store (not a big box store, like petsmart or petco) should be able to advise on what fish are suitable for which sized tank.

Also, your beneficial bacteria lives in your filter. If your filter relies on those “disposable” cartridges, then youa re throwing away this good bacteria each time you change them out, which can lead to water issues. I advise swapping over to one that can be filled with ceramic noodles.

It’s anything but HELPFUL to insist on YOUR preferred way of quantifying KH “I prefer to use degrees of carbonate hardness (dKH).1 dKH is about equivalent to 17.9 ppm.” when the API Master Test Kit and Test Strips (and every other one) use ppm. Seriously you don’t see the math errors you’re inviting? And how difficult would it be to just extend your CHART to include ppm?

Hi Alyr,

You are incorrect here, not every test kit measures in PPM, nor do tools like dKH Colorimeters. However, I will take your advice on board and fix this up when I update the article.

Great article! I just have a quick question, I cannot for my life of me get me tank to cycle and I was told to check my KH. I have a Rio 450 run by an FX6 and it doesn’t seem to break down ammonia, it only seems to rise and never break down into nitrite ect. Could KH be to bo blame? Any help would be massively appreciated.

Hi Jordan,

Kh only needs to be adjusted if your pH is is either lower than you would like or swinging wildly.

Have you checked out my cycling guide for more advice? It’s helped hundreds of people successfully cycle their tank. You can find it here.

So I have an Oscar and a pleco in a 29 gallon tank, I realize I will have to eventually get a larger tank as the oscar grows but hes still little right now. Anyways, I tested the levels tank. No ammonia, no nitrates, no nitrite, but our water is soft(75 ppm). The pH level is 6.8 and the alkalinity is showing low(40 ppm). The pH indicator is sgowing the pH is in the neutral levels. Would it be beneficial to try to increase the alkalinity of the tank. I just dont want the pH levels to increase to a danger zone. Also since the water is soft would that be a cause of low alkalinity? I’m new at being a fish mom and just worried about my Brutus. Yes I name my fish! Lol

Hi Janie,

Firstly, Brutus is an adorable name for a fish!

If you are not reading measurable levels of nitrate then something is possibly wrong – except for a few unusual circumstances, it should continuously rise. One of the reasons we perform the weekly water change is to reduce these constantly rising levels of nitrates.

Did you cycle your tank before adding your fish?

Your tank very likely is overstocked, especially if that’s a common pleco but it sounds like your head around this with getting a larger tank.

Soft water is low in kh by nature. Ordinarily, you would only raise this if you are noticing rapid changes in pH. If your water is soft as you say, then this is a possibility. Unfortunately, you’ll need to measure with your test kit and react accordingly.

Thank you for replying!
We cycled our tank for a month before adding fish. We made the mistake of adding goldfish into a new tank and they died the next day. So we let the filter cycle and build the beneficial bacteria the tank needs. We added a moss ball type plant, because the guy at the fish store said that would also help cycle out the bad bacteria. The fish seem in good health and swim all over the tank, again just wanted to make sure that tye low kh wouldnt effect the fisges habitat if the ph was stable.
Thank you for your informative article and reply, it really helped me understand.

You mention baking soda will stabilize the pH at a higher level. Is there a different element carbonate which will induce a stable low pH, like 6.5? In other words, which substance would give me an ok KH and low pH at the same time? I’m looking at Amazonian fishes, so a low GH would be important as well.

Most sites recommend naturally released tannins as the only acidic substance to be used, but I’m sure there must be other acids and/or buffers that wouldn’t hurt the fishes.

Hi Luís,

Seachem actually makes acid buffers for this very reason. You would need to research what those contain.

For a while now, we have been using bottled RO water for doing water changes. Because we have added a new tank (and a couple more are in the works) we want to switch over to using city water. I ran a test strip and found that straight out of the tap, the GH is 25ppm, the GK is at zero, and the pH is at 6.2. I have some Seachem Equilibrium for the GH but want to make sure that I should be bringing all the parameters up to my fish’s needs before I add it after a water change. Is this correct?


Hi Steven,

Yes, you are correct with your thinking. If you were to add it to your tank aftert the water change, it gives the chance for the parameters to swing, which can shock your fish.

I also highly recommend using an aquarium test kit (I personally recommend the API master test kit for anyone starting out) as it will give you a more accurate result as to what you are working with. Test strips can often give incorrect readings and are more expensive in the long run. Also, make sure you read your results under natural daylight. Indoor lighting can throw the colors off.

I have recently (8 days ago) setup a 125 gallon aquarium as a tetra (Diamond, Gold, and Neon) only tank…no fish have been added to the tank yet.
Have been using the API master test kit and have been noticing my KH is slowing rising. Used RO water with no added chemicals such as Neutral Regulator or Equilibrium to attempt to lower my KH without success. Then switched to RODI water using the same process as RO water and was unsuccessful in lower the KH. On saturday morning the KH was at 18 dKH now it’s at 23 dKH.
Will adding “pure water” to my tank (with the current parameters below) actually create more carbonates/bicarbonate as the water chemistry is being altered at the molecular level? As I am trying to get the pH down and stabilized between 6.8 – 7.2. There are currently 15 medium sized IAL’s and also had created an Indian Almond Leave Extract using 8 leaves in a 2L container and had not seen a decrease in KH either.
Current parameters in the 125G as of 8/11 are:
pH = 7.6
H.R. pH = 7.4
Ammonia = 0
Nitrite = 0
Nitrates = 5.0
GH = 6
KH = 23

The only items in the tank are Indian almond leaves, manzanita driftwood, Eco-Complete and live plants (pennywort, anubias sp., and java moss). Keeping this a very, very low tech planted tank. No fertilizers have been added to the tank either including during the initial setup.

Completely baffled, stumped and frustrated on how to proceed, if I even should proceed. Almost getting to the point of tearing down the tank and giving up! Any advice, hints, tips will be much, much appreciated. Thank you in advance for your time, energy, and support into this matter.

Hi Paul,

What are the parameters of water straight out of your tank. If it’s lower than the readings inside your tank, then something inside the tank is “leaching KH” into the water, causing it to raise. Is this a possibility? If it is, removing the cause could stop the KH from rising.

I did have one (1) rock in there but had removed it to conduct an acid test using white vinegar which the rock had no reaction or no bubbling to the vinegar. Have not put the rock back into the tank.
The parameters of my RODI water are:
pH = 7.0
H.R. pH = 7.4
GH = 3
KH = 3
TDS = 56 ppm

The TDS in the 125G is 147 ppm. Is it possible the driftwood could be causing the KH to increase?
Did forget that I had added 125 grams of ST International Aqua Soil. According to the manufacturer, the soil has a pH value of 6.7 – 7.0, could this be cause of the increase in KH?

Hi Paul,

Sorry, I just want to clarify this to make sure I’m on the same page, are you using pure RO/DI directly in your tank without remineralizing it? Is this the “tap water” you are adding?

No I do not use tap water to mix with the RODI water. Tap water is used only in the Axolotl tanks and use Seachem Prime or Safe to treat their water.
When using RODI water for the planted tanks I use Seachem Equilibrium and for the non-planted tanks, I use Seachem Replenish.

Got it. Thanks for clarifying. So the reading of your tank on the KH front is considerably higher than the remineralized (equlibrium/replenish) water that you have tested before adding it?

If so, something in the tank is almost certainly possible. I’m not sure it would be the driftwood, since these release tannins that are acidic and should reduce KH. Often, it’s a case of trial and error (remove something, check if it made a difference for a week, try removing something else etc.)

Hi, I have a 200 L tank with a handful of neon tetra, 3 platys, 2 cherry barb, 2 corys and a male and female pearl gourami.
My PH and GH are good, but KH high, but after reading this, I’m worried to reduce the KH incase the PH drops. What’s my best course of action? Also my carbon dioxide is a tad on the low side, how do I correct these problems?

Hi Sammy-Jo,

You don’t need to adjust the KH unless it’s unsuited for your fish.

I assume you have a planted tank? To increase it, you would inject CO2 into the tank, that’s a whole other ball game and may not be necessary depending on your setup.

This is a great article. Quick question – I have a 150g saltwater tank with Tropic Eden Mesoflakes as substrate, which is 100% aragonite. I have been having issues of my alkalinity increasing on it’s own – every time I do a water change (fresh mixed saltwater is at 7.8 dKH) it goes back down to low 8’s dKH, and then over the next few weeks it creeps back up to 9+ dKH. It keeps happening over and over. I am not adding anything else to the tank. Do you think it could be the substrate that is causing the alkalinity increase?

Hi Scott,

It’s difficult to diagnose causes online, but if your substrate is aragonite then it certainly is a possibility. It’s one of those things where the only way to know for sure is to remove the substrate from the tank and monitor your readings. Unfortunately, substrate is probably one of the most annoying this to remove from a tank that is already set up – you’ll want to make sure you have ruled everything else out before doing it, just in case.

Hi Ian hope your well, just when you think everything’s going smoothly! As you know I’ve been doing daily testing using the nt labs test kit ( bought a month ago long expiry date ) my nitrates show to be very high , even diluted 1 part aquarium water with 4 parts tap water ( no nitrates ) and still had a reading – my problem is a friend gave me a api test kit today expiry 2020 tested nitrates and hardly any less than 10 it’s like a tan colour , can’t believe that two reputable test kits show 2 completely test results to the extreme, just wondered if you had any idea what can cause this have done it 3 times each one the same.

Hi Andrew!

There could be a wide range of different reasons tests use different reagents. For instance, different tests using different reagents, in different concentrations which can react differently according to what has been added to the tank.

I generally recommend API on this blog as from my experience they are always inline with my much more expensive salifert test kits, at an affordable price.

The only way to know for sure which is right is to get a second opinion from your local fish store, who should also offer water testing as a service (avoid the big box chains like petsmart or petco)

Just to confirm, you are reading each kit in natural day light? indoor lighting can severely throw off the results.

Hi Ian sorry I see you replied to my original query, thought I hadn’t posted it by mistake! Yes it’s the api kit my friend gave me I read them on my balcony in day light , will go to local aquarium shop at lunchtime and get it tested there see what they say ( I live in the uk ) will let you know what results are.
Many thanks

Hi Ian just re tested water using the api ammonia 0.25/0.50 nitrite anything from 2 to 4 nitrate 10 ( light copper colour ) the ph is 6.4 – it’s day 16 now haven’t redosed with ammonia since Saturday as it seems to have come to a stand still , should I do a 25% water change ( haven’t done one yet ) to try bring ph up .
Thanks for the help complete newbie to this !

Hi Andrew,

I think the first thing that needs to be done is figuring out which test kit is telling the truth. It’s going to be hard to follow the cycle as you generally react according to the test kits results. The wrong results could lead you to take an incorrect action. I hope the local aquarium sheds some light on the issue!

The waterchange won’t hurt. Just be mindful that it will reduce your ammonia, nitrite and nitrate by a similar amount (e.g a 50% water change would roughly reduce each by 50%) If you do one, you will want to redose your ammonia to the appropriate level after.

Hi Mr.Sterling…thanks God for this explanations. I burn my eyeslashes trying to understand the marriage between Mg, Ca & Kh. I just need to read ur article and i got it. Thanks for write it..

Hi. I have a 16 gallon that’s giving me a headache. My tap water is soft. pH 7, KH 2, GH 4.
My tank has inert decorations and substrate, and usually pH 7.0/KH 2. I added some activated carbon to filter out some planaria medication, and also lowered the temp from 27c to 24c (Added Caridina shrimp) and those things made my KH increase to 3 and pH to 7.5.

I have decided that KH 2 is too unstable, and want to increase it to 4 (Tetras and Shrimp), to get a stable pH. Do you just to a waterchange and add KH+ salt or do you mix water and salt before you add it to the tank, during waterchanges? I don’t want to shock my fish. Already lost 2 fish and 5 shrimp during the last fluctuation. It just means I would lose the ability to use the Aqua in/out system, and have to use buckets again. I also have a CO2 system, so my pH fluctuated between 7.0 and 6.5 (peak concentration), but now it’s 7.5 even with the same ammount of CO2 as before. I’m guessing it will lower a bit when I remove the charcoal aswell.

It’s a pain. Increasing KH will also Increase pH, which is allready high. Then I have to bring it back down to pH 6.6-6.9 using CO2, without killing my fish. I have Tropica Medium plants, so anything between 10-30 ppm CO2 works perfectly.

Hi Robin,

I’m not sure if you have already seen this guide, but it will answer most questions on KH from a beginners perspective.

Although, based on your description, it sounds like you have your head around what it is you need to achieve and the role KH plays in that.

For the buffer, you would add it during the water change. The KH in your tank shouldn’t have dropped so much that adding buffers during the water change will spike the KH of your tank once added.

As for your Aqua in/out system, you can run from the tap to a bucket, add your buffer then pump from bucket to tank. A cheap water pump will set you back 10-20 dollars, you don’t need anything big for this purpose.

Balancing KH while injecting co2 is a huge pain in the butt. Unfortunately, if you want to keep more difficult plants, it’s the only real option.

Thank you for your reply! 🙂 I didn’t see it until today.

My tapwater is pH 7.0, KH 2 dH°
Tank is pH 7.5, KH 3 (“inert” rocks)
Added 0,8 grams pH/KH+ salt and the tank became pH 8.0, KH 4.
After 3-4 days it’s pH 7.5, KH 3 again. Haha. What a pain.

I was hoping the KH would stay the same for at least during between weekly waterchanges. My CO2 is still barely being injected, because I’m scared of what will happen if I stabilize pH at, say 6.9, using CO2 and then KH drops 1 degree after 3 days.

I have also considered buying a 40 litre water tank and adjust the water there, but the same KH drop would probably still happen, after a few days. Even with RO water.

So now I’m arguing adding crushed coral vs. dosing KH salt 2 times a week. Not sure what’s best.

Unfortunately, it sounds like you are dealing with some very soft water. It’s difficult to know which path to go down since a water source can vary so much from location to location. If I was in your shoes, I would experiment with adding crushed coral. It could improve the KH baseline enough that you may be able to get away with dosing KH buffers once a week (or ideally none) there isn’t really a “best” out of the two. It’s hard to balance crushed coral since the amount of KH it leeches back into the water will vary. You may need to add more or less to see the desired changes. KH Buffers on the otherhand allow you to dose a specific amount and achieve an expected result.

I know it’s not what you want to hear, but the other alternative is to stock plants and fish that suit a softer water.

Hello, Mr. Sterling

I’m a beginner and have been studying for a while in order to assemble a nice aquarium at home. My tank is a 45 L one, I intend it to be a low tech planted aquarium (no CO2, but with nice cannister filter, substrate and a chihiros led lamp A501) with tetra neons (around 6 of them) and maybe 5 dwarf corydoras. My tap water is PH 7 (sometimes 7.2), KH 1 and GH 3 and I still don’t know for sure how to deal with water parameters after cycling is finished.

I need to reach a PH of 6.8 for my stock, GH is kinda ok for them since neons and corydoras enjoy soft water, but I think my KH is very low. Since I want an acidic PH, is not adjusting KH really a problem? I thought about using Seachem Carbonate to raise my KH without affecting PH and maybe use Acid Buffer to keep it on 6.8 (i.e. after cycling and verifying the stabilized parameters). Am I at the right path here?

Thanks in advance!

Hi Angela,

Excellent question.

Generally speaking, both of your fish should be fine with a pH of 7. Keeping the pH stable rather than exact is in my opinion a better outcome for most fish, as long as it’s within their tolerated range.

While your KH is on the low side, it’s only a concern if the pH is dropping before the week is out – your weekly water change will replenish the little pH and the KH that is there.

Test daily and monitor how your water KH and pH changes between water changes. If you can get away with leaving it as it is, fantastic – you won’t have to spend money on buffers or extra time balancing the water for pH and KH (which can be a mission in itself)

Hey Ian – I’m excited to find pages on KH and GH. Water chemistry can be such an interesting aspect to aquarium-keeping.

Do you have the conversion rates for degree to mg/L (or ppm) for KH and GH handy? Thanks.

Also quick site feedback: Boy, did I have to scroll way down to get to this comment section. Maybe collapse the conversations or place this section above the convo.

Happy aquatic sciencing – J

Just want to make it clear that nitrite and nitrate aren’t acidic. The byproducts of nitrifying bacteria are in the fact that they product carbonic acid and consume alkalinity from the water when they break down NH4 and NO2. Only when NO3 can be denitrified, water molecules are destroyed and thus making H3O, and thus buffering the carbonic acid. I would not recommend this for aquariums. Let your plants, algae, and water changes take care of the Nitrate. Only dissolved oxygen levels of 0.5 mg/L can support proper denitrification.

Hi Seth,

Thanks so much for weighing in. In order to help beginners, I keep things as simple as possible – many beginners struggle with the basic chemistry as it is. I try not to confuse things where possible.

I really appreciate you taking the time to explain in further detail!

Hello I’m new to the aquarium hobby and being all serious with water parameters . But I have a shrimp tank and these guys are fussy lol dwarf shrimp to be exact . Well my question is I don’t know how to understand to gh kh results . I basically got 10 drops for gh test tube to change color and 4 drops for kh . And because I don’t understand the results I’m unable to help my red yellow and blue neocaridina shrimp and green caridina shrimps. I’m not even sure what the proper gh kh ratio should be for them I researched everywhere lol. Please help thank you so much 🙂 .

Hi! Thank you for all of this information!

I have a 20 gallon freshwater tank, no live plants, gravel in the bottom, a few fake plants and decorations along with an aerator (, heater (77.2 degrees) and a Tetra Whisper 20 filter ( using disposable filter cartridge with activated charcoal (

There is one 3-4 inch goldfish, one 1.5 inch black molly and two 1.5 inch Mickey Mouse platies in the tank.

Test results (API master test kit and API KH/GH test kit:
KH-16 dKH
GH-5 drops
High Ph-8.4

A 20% water change was done using 3 gallons of tap water and 1 gallon of RO water. 20ml of Quick Start, water conditioner and 1 Tbs. of aquarium salt.

Tested the KH again the next day and KH is still 16 dKH.

I tested our tap water that same day and the KH is 18 dkH and our RO water is 8 dKH. The RO filter was changed a few months ago and it might be due for a change. That might be the reason there is still a KH of 8 dKH in supposedly “pure water.”

According to the API KH/GH test instructions, the fish we have need between 6 and 11 dKH. I’m thinking I can use straight RO water in the tank without mixing with tap water. I want to gradually switch out the water from tap to RO but I’m not sure how slow I need to go to keep from shocking the fish. What percent water change would you recommend and how often? Is it even a good idea to use straight RO water?

Thank you!

Hi Diann,

RO water will need to be remineralized. You can’t use it straight or it will kill your fish. Fish use a process called osmoregulation to draw nutrients and trace minerals out of the water. Unfortunately, RO water doesn’t have any.

Good morning and thank you!

So, I will have to use some tap water along with the RO water or supplement the minerals. I guess I’ll have to figure out what ratio of tap water to RO water I can use without skyrocketing the KH to over 11 dKH. I’ll do that in a bucket and just mix and test until it’s right. That is unless you have an easier way to figure it out.

Thanks again!

Hi Diann,

If you are not using chemical buffers, which can be measured out specifically to stabalize pH and KH, it’s very much a game of trial and error. The good news is that once you figure out the ratio, you likely won’t need to change it!

Hello! Fascinating article and I’m trying to figure my water out as far as keeping freshwater fish. I live on a private well that has never been tested or treated in any way, do not have a water softener or RO or anything. My testing straight out of the tap (cold water) gave me 38 KH and 2 GH. I do not have a new pH kit yet, but the last time I tested it on this water, it was around 8.5.

Are fish ok with that high of a KH since it’s just a buffering capacity and means my pH is just VERY stable? Or is there a maximum range that fish will start to do poorly in?

For my GH, I realize this means my magnesium and calcium is very low, and if I want to have snails or shrimp, I should increase it slightly. I have been looking at a GH booster for this purpose, as I would also like to have a few live plants.

Have you seen water parameters like these before? I swear I did the testing correctly, and that there are no water treatments on this well. Thank you for your insight!

Hi Kama,

Are you able to re-test GH. It’s usual to have a KH that high and a GH that low.

A High KH generally means a high pH. And 8.5 is certainly on the higher end. It’s only going to be an issue if you want to keep softer water fish, since you will forever be trying to buffer it with chemicals to lower the KH and, by association, pH. In these circumstances, I generally recommend a fish that suits your water, so you don’t have to adjust the water.

Cichlids in particular are popular choice (and in my opinion, stunning) fish that would thrive in your water.

Hi there, I want to ask something, in my tank, I want to keep my KH around 5-6 dKH (some plants prefer soft water like tonina, eriocaulon, etc), Im using RO water for my water change every week and its 50% water change, KH of RO water is 1 dKH, after 4days of water change my KH in tank build up to 8dKH, and its consistent until next water change, do you know what’s wrong with my tank? And should I using acid buffer for my tank? Thanks before.

Hi Tommy,

It’s really hard to diagnose your tank over the internet. It sounds like something in your tank may be leeching KH into the water, resulting in the rise. Unfortunately, this is often a case of trail and error, removing one piece at a time until you find the cause and the KH stops rising.

Hello Mr Ian!

I hope all is well. I just did a water test on all 4 of my tanks and

Timmy (10 gallon)
Ammo: 1ppm
Nitrite: 0ppm
Nitrate: 0-2.5ppm
pH: 6.0

On the 24th his readings were
Ammo: 1ppm
Nitrite 0
Nitrate 0-2.5
pH 7.2

( I have NEVER had ammo readings in his tank as I’ve had him about 8 months and believe he’s cycled. I don’t know why the sudden PH swings. That isn’t normal at all. In 5 days it went from 7.2 to 6.0 and its very light so with the API master kit only showing the light yellow even if it’s below that scares me.

I have the neutral regulator and alkaline buffer however since the ALK buffer says it raises PH and the neutral regulator says to adjust ph to 7 while removing chlorine chloramines & detoxifies ammo, I’m not sure which to use.

I do understand that if I use the neutral reg to get my PH to 7 if my KH isn’t on point then getting it to 7 won’t last so I’m thinking I need to test my KH first and then that would determine which one I use?

I had a very low ph in champs tank about a month ago and I used the alk buffer and his has stayed between 7.2-7.6, just now its 7.6 so that seemed to work….

Diamond (4 gallon)
I got her to replace my poor sassy. Her readings seem to be doing just great as for the way you describe how a fish in cycle will go.

Ammo: .50-1.0ppm
Nitrite: 0
Nitrate: 0
ph: 6.0

added the alk buffer

Ammo: .25
Nitrite: 0
Nitrate: 0
pH : 6

so in conclusion, I would say the results are not consistent. it worked great for champ but nothing for her. By the way, her tank had 5ppm nitrites about a week and a half ago but I did water change and have been testing and priming every day so I’m finally in the stage of the cycle where ammo is not rising as quickly – no nitrites – nitrates have been present but now they’re gone so I think I have a ways to go but I need to get her ph UP and I need to find the remedy for these tanks to get up and STAY up.

I know you said the directions are very basic on the KH and GH kit but I am a little confused.

– add KH solution 1 drop at a time, making sure to count the number of drops added. Cap and invert after each drop
– The test is COMPLETED after shaking the water in the test tube and it turns from blue to yellow
– This is where it gets a little contradicting – it’s just stated the end of the test ould be when the test tube turns blue however the last step states: To determine the KH value total the number of drops that must be added to turn the water BRIGHT yellow.

(i understand I need the water to turn yellow from blue… however, would I keep adding drops at this until I get a BRIGHT yellow? I have tried the test once before and when it turned yellow is was SO pale like the 6.0 ph pale yellow so I don’t think that would be the completion of the best LOL/

I’m so sorry I always come to you with so much confusion, I am just really bad at numbers and am totally new to this hobby Timmy was my first 8 months ago but I have fallen in love and am trying my absolute best to follow the advice of your article before bothering you with questions.

By the way, what would you suggest about the sudden 1ppm ammo in timmys tank? I am dosing with prime but I would think that since its 8 months and a cycled tank would convert the ammonia within a few days even though it’s probably because (the tap water had a 1ppm reading always) but since he was always at 0 and my water wasn’t something is off and I promise I have changed nothing! Do you think I could have stalled his cycle with the swinging ph, along with changing to much of his filter media by accident? I’m thinking about tosing with TSS and recycling since I have never gotten nitrates rising anyways this might be a good idea, what do you think

UPDATE that might be helful. I just did the KH test the way that made sense to me and that was adding a drop until I got what I would say is bright yellow. It took 9 drops so that would be 9DKH and thats in timmys tank with the 6.0 ph that has dropped for no reason… is there other reasons my ph would drop if i have a KH that is in the correct range?

Hi Again Dominque,

You do the test until you first see yellow. This can be difficult to spot, I find using a white sheet of paper as a background helps.

If your pH is dropping then there is a possibility that your tanks are not cycled. To put it super simply, during the process of turning ammonia -> nitrite -> nitrate, the beneficial bacteria give off acids that reduce pH. Otherwise, if your KH isn’t too low, you would need to look for another cause.

The 1 ppm in Timmy’s tank would suggest that either the tank isn’t cycled or somewhere along the line the cycle has crashed.

Once again, I really must insist that you get help from either your local fish store (not petco or petsmart or similar big box chain) or a local fish club. They will be able to provide actionable guidance – it really is nearly impossible to trouble shoot the issues you are facing online. I think a face to face approach here would really help sort out some of the confusion you are experiencing.


I am new to the fish keeping hobby, and can’t wait to get started! I recently bought a 56L (UK) glass aquarium and have it all setup. I have setup my tank with substrate rocks etc… and added the water. Over the past few days, I have been adding the required chemicals to make sure that my tank is fish friendly! However, yesterday I used a water test kit in my tank. The results turned out to be all green except from the KH and GH. I found that these two were in the RED. This made me panic as I want to get my fish as soon as possible. Please could you tell me some of the easiest and cost effective ways of lower the KH and GH.

Thank You.

EXTRA INFO: Apologies for not mentioning it before, but my tank is setup to be a tropical aquarium. I am looking at getting mollies and neon tetras with living plants.

I would appreciate some help. I have a Bio Orb 60l cylinder tank which I started in November, I had 10 guppies but have lost 4 already. I’ve been testing and my Kh is quite high between 15 and 20 but my Ph is around 7.2, everything else is ok. I would like some advise on what to do about lowering the Kh if needed and also could that be what’s killing my fish. I’m so gutted losing my fish. Thanks

Hi Jane,

Did you cycle your tank before adding your fish? Also, when you say everything else is okay, what are your ammonia, nitrite and nitrate levels? Also, how often do you perform a water change in your tank?

I cover lowering the KH in the article above. As for if it’s what is killing your fish, it’s difficult to say without the above test results.

Hi Ian,

Are there any instances where KH can be too high? For example, my tap water is 14 dkh which is outside of the ranges you’ve got for most kinds of tanks (our main one will be brackish so that should be fine).

It seems like having a high KH is only a good thing unless you need to lower the PH?

To put it another way.. is my water unsafe for a tropical fish tank?

Thanks 🙂

Hi Stuart,

That’s a complicated question. To be honest, it entirely depends on what you want to stock in your tank. An excessively high KH would see similar issues to an excessively high GH which I cover here:

Of course certain fishes are more or less tolerant. Many shrimp for instance prefer water at the bottom end of the KH scale and die in harder water. If you google “[species] care sheet” you should see the KH requirements listed as long as the other recommended water parameters.

I have RO water but in your article on water sources, you wrote that RO water needs to be remineralized so I have never used it. Is it safe to use it straight on my tanks (freshwater)

Hi Tom,

RO water is unsafe to use straight as it does not contain the KH and GH needed to maintain aquatic life. It can be used to cut hard water (mixed with), but it can not be used alone.

Thanks to you I bought a kit and started checking KH. My tap water kh is 5. As I inject CO2 it rises. My question is: Which kH reading I use as a baseline to measure pH against to monitor my CO2?

Also, I’m 3 weeks into a fishless cycle in a dirted tank with plenty of young plants. The Miriclegro organic dirt’s capped with 1/2 inch of gravel. The ammonia ranges from 0 -.5, Nitrites 5 -10, and Nitrates 5-10. Even after a 50% wc the nitrates barely budge, and the ammonia may increase slightly with a slight drop in nitrates. I’m thinking the dirt is pushing the ammonia, but the nitrite isn’t budging. What are your thoughts? I’d like to start my fish before the second coming.

I’ve had my 20 gal tank up & running with 1 guppie, 5 platys & 2 tetra for a little over a month. My ph is 7.6, ammonia is 0, nitrite is 0, nitrate is 0, kh is 22 & gh I quit adding drops at 25. I’m using API freshwater master test kit & API kh & gh test kit. My water is a little cloudy & my fish are staying at the top of the water. What do I need to do??

Hi Dena,

Did you cycle your aquarium before adding these fish? And are you reading your test results in natural daylight? Indoor lighting can make the colors look off and lead to an incorrect result. Also, a nitrate of zero typically indicates a problem in the tank, such as it not being cycled.

Hello Mr. Sterling , I from malaysia ,I just start the hobby, I got a 20 gallon tank with 9 crown loach , after seeing your explanation on kh and ph, I fast do a kh,ph test using api test solution , i do water change and test the water ph in 7.8 and kh is 2 , i also buy searcham alkaline, acid buffer …i get little confused on how to use this product..for clown loach need ph at 7 and kh 8 , .. I need o lowering ph first or buffer kh

Hi Calvin,

The focus should be more on getting a stable pH than a precise one. To this end, I would add the alkaline buffer to bring the kH to 4. While 7.8 is on the edge of the prefered pH of clown loaches, they should be fine if it’s stable and all else is consistent.

Please help my tap water kh0 gh2 at the moment.
Betta /corrie/ pleco /tetra
No substrate atm but wood in tank
Best way to increase and how to do it safely?

Hi Mykl,

Thank you, this feedback means the world to me as the goal was to make this easy to understand to newcomers to the hobby.

Hi Ian. I just set up a new tank and tested filtered water from my tap with a 5 in 1 test strip before filling the tank and everything checked out. I bought 4 fish after letting the tank run for a day. Once they were acclimated to the temp in the tank I put them in the water. All 4 we’re dead in 3 hours. I checked the tank water with another 5 in 1 strip and all the parameters were within expected limits except the KH which was off the charts above 240ppm. On a whim, I took the same strip and retested the water directly out of the filtered tap water and the KH came down to about 40ppm. The tank is set up with typical aquarium rocks, plastic plants, filter, air stone, and heater. I have had more than a few tanks in my past without any problems and before there were all the ways to test water quality. Any idea what in a new tank would affect KH so much in what is otherwise acceptable water?



Hi David,

Did you cycle this tank? Not cycling the tank would have been the bigger issue here if you skipped that part.

Thanks Ian. I was trying to cycle the tank with the fish. I used a few barbs which I understood could be used for this.

Anyway, I have since changed the water out. The same issue exists. Fine out of the tap. High KH in the tank. What do you suggest to cycle the tank before introducing fish again? Should I just focus on this or try to lower the KH at the same time?


Hi David,

I’d personally just work with your high KH. Balancing KH is an ongoing and expensive task as you have to constantly buy the buffers needed to adjust it. My preference is to choose fish that are suitable to the KH in your tank – there are plenty of stunning hard water fish to choose from.

On the cycling method, the best method to cycle a tank is to do a fishless cycle:

Fish-in cycles are not really the done thing anymore – you are essentially killing fish to get a cycle started. The fishless cycle is better is it is both humane and allows you to accurately measure and record the cycle process.

Thanks again Ian. I will set the tank up with the fishless cycle method you advised. One last question on your thoughts for why the filtered water would be ok out of the tap, but the KH would spike once in the tank. Any ideas?


Hi David,

It all depends on what is in your tan, something could be leaching KH, such as limestone. I have observed some instances where KH increased when tapwater was left to sit, you can test this yourself by leaving a glass to the side for a few hours then testing it.

I have a problem with KH in my tanks, even though my pH is fairly stable and on point. Is there anything I can do that will raise the KH but not affect the PH?

Hi Ian,

I am a few weeks into the fishless cycling process on a 10 gallon fresh water tank. Currently, daily testing has nitrites testing at around 2-3ppm and consuming nearly all of the ammonia I add, but nitrates not yet high enough to consume the nitrites.

I am using pretty much all tap water which naturally has a very high kH and pH – kH around 22 and pH around 8.

This is also an aquaponic tank, with plants in a separate planter at the top that the water is pumped into for 10 minutes every hour. The roots act as the filtration system.

My kH keeps dropping dramatically – down to near 0 in a few days time, which causes my pH to drop below 6 as well. 5 days ago I did a 50% water change, which brought both the kH and the pH back to normal. This morning’s tests showed kH down to 0 again and pH at 6, which is stalling the cycle again.

What could be causing this, and how do I keep it stable? Is it just a matter of more water changes, or do I need to add a buffer?

Thank you!

Hi Vanessa,

That’s really unusual that you are getting such a low kh. What happens if you leave your tapwater out for 24 hours, does it experience the same reduction in Kh?

Hi Ian. this is a great article! Thank you!
I live in Switzerland which water is sourced from lakes fed by limestone mountains. I had my tap water and tank water tested at local aquarium shop and the values were KH 12 and GH 5, PH is 8.2 for both. I have a 110L fully cycled tank of 4 months age now – ammonia,nitrites and nitrates are all 0 for past 2 months. I have Neon Tetras (14), Guppies (14) and Cherry Shrimp (3) and Zebra Snails (2)
Does the hardness levels sound correct to you (where the KH is so much higher than the GH)? I have been trying to lower the KH at the advice from the aquarium shop to make the water PH better for the Neons by doing 50:50 distilled water/tap water changes every fortnight over the past 2 months but only got down to 8.0PH and then the guppies started to get fin rot in past 2 weeks.
I was going to get a KH and GH test kit as we are in self isolation for the next 2 months.

Hi Ann,

It’s hard to say what normal is as local water sources vary to such a degree. However, you do have fish there that prefer slightly softer water. My advice is to typically stock fish that suit your water source. This way you don’t need to spend time balancing the water which can be difficult and quickly lead to errors.

I had a ph spike that killed my shrimp and my betta isnt as active as he usually is. My normal PH is on the high range anyways.. 7.8-8.0 but now its reading 8.8. All of my shrimp are dead. I’ve had them for 3-4 weeks and they’ve been doing great until a few days ago. I have 2 anubis, 1 java fern, 5 marimo, 2 IAL. 10 gallon tank. The plants are glued to aquarium rock with super glue gel. I added IAL a few weeks ago and the plants around the same time. I originally had all silk plants. I noticed my shrimp were not very active the past few days. I’ve have had this tank since January and use soring water since I have extremely hard rusty water pre softener.
I know there are ways to ultimately lower Ph, but trying to find out why the sudden spike

Temp 79.7
Ammonia 0
Nitrites 0
Nitrates 20
Kh 13
Gh 18

Any help would be appreciated. Thanks in advance!

Hi Heather,

Shrimp typically prefer a lower KH and ph. As do betta. I typically recommend buying fish that are suitable for your water source. Otherwise you need to constantly by adjusters and attempt to balance the water quality, not only is this costly, but a single mistake (overdosing or forgetting to dose) can cause your fish to become stressed and die. Everything else looks normal on the parameters, but they are not suitable for softwater fish.

Greetings! Is there an online program to enter water parameters? Seems an easy enough program. The API instructions are poorly written. No issues except plants are starting to loose color. Tank is stable for ages. Just wanted to get more data.

My data and setup are below:

10 gallon freshwater tank.

24″ flowerbed over the top of tank, filled with Lava rock and ~20 plants (herbs, basil, chard, arugula, etc.)

Submersed pump with sponge filter goes up, and pours over a 3″x3″x1″ mesh bag of Zeolite/carbon blend.

14″ knot of driftwood

various plants: java moss, marimo, Microsword (Lilaeopsis brasiliensis), baby-dwarf tears (Hemianthus callitrichoides), Monte Carlo (Micranthemum tweediei), Creeping Jenny (Lysimachia nummularia), Selaginella wildenowii, and a very few of the almost unavoidable floating duckweed.

cuttlebone (~1″x1″ piece)

1″ substrate: black gravel on a <1/2" layer of expanded and settled coconut fiber. no floaters, clean top of gravel.

LOTS (probably too many) nano-fish: target is Bluestars, but also have a dozen orphan fish.
10 Blue star endlers (looking for more females)
2x Green Kubotai Rasboras,
3x rummy nose tetra,
1 phoenix rasboara,
1 black molly,
2 white cloud,
2 longfin danio,
1 yellow glo-danio,
2 red glowlight tetra,
1 gold barb,
1 female blue guppy
1 panda loach Yaoshania pachychilus)
1 nirite snail,
3 nano-shrimp.

All fish are healthy, no nipping, no chasing. Friendly tank.

All fish were quarantined and treated for a month in a separate tank. Fritz Paracleanse, Maracyn(Erythromycin), Ich-X, and deworming flake food on 3 cycles of 3 day series, 7 day break, and 1 drop of tea tree extract per gallon every month.

Ph very stable at 7.54 (digital, calibrated monthly)
Water change ~25%, every 7-8 days.
No algae issues.

tested after 10 days (skipping the weekly water change for data's sake).
Ph 7.54
KH = 6 drops
GH = 8 drops

3 days after water change:
KH = 6 drops (API 5ml liquid test)
GH = 6 drops (API 5ml liquid test)
zero ammonia, nitrates, nitrites.

Water is either gallons of grocery store "spring" water, or Suamico, Wisconsin tapwater run through a britta filter and set out for 3-5 days before using in a tank.

Plants are showing signs of white. Perhaps too many plants from the aquaponics.

Question 1) I have no idea if the KH/GH are okay for this setup. Any thoughts?

Question 2) Wondering if I should supplement the water (iron, magnesium sulfate…). Thoughts?

Question 3) any other comments, thoughts, suggestions, or things I should watch out for?

Hi Kirk,

Thanks for the detailed writeup!

My Biggest concern would be the size of the tank for that many fish (the one inch per gallon rule is bogus)

My other concern is your lack of nitrates. In a cycled tank, typically, nitrates should forever be rising. Now it is possible that your plants are absorbing this, but given the number of fish, I would probably expect to see a measurable level.

Most of those plants are fairly low maintenance If you are using aquasoil or similar, you can probably get away without dosing nutrients

Also, is there a reason why you are not using tapwater and seachem prime. It is by far the easiest solution when it comes to water changes, cheaper and easier than your current method.

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