Last update: November 28, 2023

How to Lower Aquarium GH (General Hardness) in Water Tanks & How to Raise it: A Beginner’s Guide

Our final chapter in our beginner’s guide to water chemistry covers GH.

GH is essentially the hardness of your water.

And today, I’m going to teach you everything about it.

Model & Make
API PH TEST KIT 250-Test Freshwater Aquarium Water pH Test Kit, 4 Piece Set
Innovative Marine Accudrip Acclimator
Aquasana AQ-RO3-RM Replacement Remineralizer for OptimH20 Reverse Osmosis Water Filter,White
Seachem Equilibrium 600gram
Weco Wonder Shell Natural Minerals (3 Pack), Small
Carib Sea ACS00120 Crushed Coral for Aquarium, 15-Pound
API PH TEST KIT 250-Test Freshwater Aquarium Water pH Test Kit, 4 Piece Set
Innovative Marine Accudrip Acclimator
Aquasana AQ-RO3-RM Replacement Remineralizer for OptimH20 Reverse Osmosis Water Filter,White
Seachem Equilibrium 600gram
Weco Wonder Shell Natural Minerals (3 Pack), Small
Carib Sea ACS00120 Crushed Coral for Aquarium, 15-Pound
Model & Make
API PH TEST KIT 250-Test Freshwater Aquarium Water pH Test Kit, 4 Piece Set
API PH TEST KIT 250-Test Freshwater Aquarium Water pH Test Kit, 4 Piece Set
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Model & Make
Innovative Marine Accudrip Acclimator
Innovative Marine Accudrip Acclimator
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Model & Make
Aquasana AQ-RO3-RM Replacement Remineralizer for OptimH20 Reverse Osmosis Water Filter,White
Aquasana AQ-RO3-RM Replacement Remineralizer for OptimH20 Reverse Osmosis Water Filter,White
Buy Now Button
Model & Make
Seachem Equilibrium 600gram
Seachem Equilibrium 600gram
Buy Now Button
Model & Make
Weco Wonder Shell Natural Minerals (3 Pack), Small
Weco Wonder Shell Natural Minerals (3 Pack), Small
Buy Now Button
Model & Make
Carib Sea ACS00120 Crushed Coral for Aquarium, 15-Pound
Carib Sea ACS00120 Crushed Coral for Aquarium, 15-Pound
Buy Now Button

What is aquarium GH?

General level of hardness, also known as aquarium water hardness, is referred to as GH for short. It’s basically the measure of the many salts that are dissolved in your water. In particular, calcium and magnesium Ions.

Water with a low GH is said to be softer water, and water with a high GH is considered hard.

So, soft water aquarium has very little or no calcium and magnesium levels. Hard water has a lot.

While GH is an important part of high-quality water chemistry, most of you using tap water don’t need to worry about it.

You see, your GH entirely depends on your purified water source. Most tap water generally has sufficient GH so that you’ll never have problems with it.

There are generally two reasons you need to monitor the GH in your aquarium:

1. You have either very soft or very hard water

If your water source is very soft or very hard, keeping certain types of paradise fish that prefer to live in the middle of this range can be difficult. You’ll need to keep an eye on your GH and raise or lower it accordingly.

2. You want to keep a specific type of fish

On the flipside, some fish thrive in harder water such as cichlids, while others thrive in soft water like discus. If you want to keep soft water fish, you need to monitor your GH water conditions.

It is also worth mentioning that since saltwater tanks use RO/DI water, they don’t have to worry about GH because the salt mix restores these minerals.

What is the difference between GH and KH?

Man comparing aquarium GH to aquarium KH

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

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

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

If you’ve ever heard someone say…

I have really hard water where I live.

They are referring to GH.

KH, on the other hand, keeps your pH levels stable.

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

But tap water is usually anything but natural…

It’s quite 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.

For more information on KH, check out FishLab’s detailed guide.

Why is aquarium GH important to your aquarium?

The number one reason why you should monitor the GH (general hardness) of your aquarium comes down to one word…Osmoregulation.

Osmoregulation is a natural process that your fish do automatically. It’s like you or me breathing, meaning it just happens.

To put it super simply, osmoregulation is the process of your fish balancing the salts and water inside their body with the salts and water outside their body.

If an imbalance occurs, it can stress your fish or worse. In severe cases, it can lead to the death of your fish.

This is why a freshwater fish won’t survive in salt water and vice versa.

There is another reason why GH is important…


You’ve probably seen this word in Gatorade advertisements.

Electrolytes is just a fancy term for minerals and salts that conduct electricity when dissolved in water – minerals like calcium and magnesium (GH!).

These electrolytes aid in muscle and bone growth, digestion, development of gills, improves resistance to diseases, and more… Pretty darn important stuff, right?

Your fish need electrolytes to remain healthy, and the only place your fish can get them is by drawing them from the water.

But here’s the thing…

Water with no GH has no electrolytes for your fish to use!

This can lead to some serious health issues.

Attention planted fish tank owners: Even aquatic plants need some degree of electrolytes. For example, plants use calcium to grow.

If you have very soft water, then the GH might not be high enough to supply your plants and fish with the electrolytes they need to remain healthy!

As you see, it’s pretty important that your aquarium contains at least some level of GH.

You should also note that the GH of your aquarium can change over time. GH can become lower in your tank because fish and plants use up the trace minerals.

Or, it could be that GH is higher in your tank because calcium and magnesium are left behind when water evaporates from the tank.

What is the best GH for your aquarium?

The ideal GH 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 general hardness (dGH). One dGH is about equivalent to 17.9 PPM.

Please note: The following recommendations are rough guidelines only. Your specific fish, plants and invertebrates may require more precise GH levels outside these ranges.

Tropical Fish Tank4-12 dGH
Shrimp Tank4-8 dGH
African Cichlid Tank12-20 dGH
Discus Tank3-8 dGH
Planted Tank3-8 dGH
Brackish Tank12-20 dGH
Axolotl Tank7-14 dGH
Pond4-12 dGH

How do you test the GH of your aquarium?

The important thing to remember is that the GH of your aquarium is invisible. You won’t be able to tell the difference between soft water (low GH) and hard water (high GH) just by looking at it.

To determine the GH of your water, you have to test it. And to do that, you’ll need an aquarium test kit. This one, to be exact…

API PH TEST KIT 250-Test Freshwater Aquarium Water pH Test Kit, 4 Piece Set
  • Contains one (1) API PH TEST KIT 250-Test Freshwater Aquarium Water pH Test Kit, including 1 bottle of testing solution, 1 color card and 1 test tube with cap
  • Helps monitor and adjust pH and prevent invisible water problems that can be harmful to fish
  • Accurately reads pH 6.0 – 7.6 and helps avoid fish loss

Don’t worry! It’s affordable and easy-to-use. But best of all, a single GH test kit can last for hundreds of tests. Just follow the step-by-step instructions for accurate results.

FishLab Note: The results of the test can be given in degrees General Hardness (dGH) or parts per million (PPM). Which you use is a matter of choice. I personally use dGH and refer to it from now on.

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

Now, you may be wondering:

How often should I test the GH of my aquarium?

Unless you have very hard or very soft water or want to keep a sensitive species of fish, most of you won’t need to worry about regularly testing your tank for GH.

However, if you do, I recommend testing it once every time you perform aquarium maintenance, such as a water change.

What happens if your GH is too high?

As I covered earlier, all tanks need some degree of GH.

But what happens if the GH of yours is too high?

Let’s look closer at three negatives brought on by high GH.

1. New fish can die

Okay, so this point is the matter of some debate. After all, you don’t have to go far to find resources that state a high GH will not affect fish as long as they have acclimated to the hard water.

Let me repeat that last point:

…as long as they have acclimated to the hard water!

But what happens if you buy a new fish and your aquarium has a significantly higher GH (general hardness) than that of your local pet store?

Well, that’s when things can turn nasty.

Generally, when you buy a new fish for your tank, you bring it home, float the bag for about 20 minutes, and then add the fish to your tank, right?

You have not given your fish a chance to adjust.

Your fish will experience what is called osmotic shock. While it can take a few days, osmotic shock can kill your new fish.

Because osmotic shock isn’t an instant killer, beginners often blame the death on the fish being unhealthy rather than their hard water.

Fortunately, there is a simple way to get around this…

Drip acclimatization

Drip acclimatization is exactly what it sounds like. You drip water from your current fish tank into a container with the water your fish came in.

By adding your harder (or softer) water drop by drop, your fish will find it much easier to adapt to the change in water hardness.

It’s a slow process, but it gives your fish the greatest chance of survival.

Want to try your hand at drip acclimatization? I highly recommend grabbing this tool…

Innovative Marine Accudrip Acclimator
  • Customize acclimation rates for any new additional into your aquarium
  • 1-2 Drips per second – for snails, shrimps, crabs, starfish, anemones

It’s almost like a gravel vacuum, but instead of streaming a constant flow of water, it removes it drop by drop and really simplifies drip acclimatization.

2. Breeding

Want to try your hand at breeding? Many fish won’t breed successfully if the water is too hard. Discus and Ram cichlids are two species that spring to mind.

The reason? In their natural habitat, these fish breed during the rainy season. As their homes flood with extra water, the GH drops.

The fish use this drop in GH (among other factors) to let them know that it’s time to start getting frisky.

So if your GH is too high, then you will have difficulty breeding these sensitive fish.

3. Live plants

Most plants can tolerate a moderately high GH or general hardness.

However, there are sensitive soft water plants that can be almost impossible to grow in hard water. Chain Sword or Dwarf Sagittarian are two plants that thrive in soft water and struggle when the GH rises.[6]

The solution is simple: Select plant species that will happily grow in the GH of your water!

How to raise aquarium GH – increase hardness

Tested your aquarium water and discovered that you need to raise your GH?

Let’s 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

Is your tap water moderate to very hard? For most of you, that will be all that is needed to increase the hardness of your aquarium water.

Simply keeping up with your water changes will be enough to replenish the GH that has been depleted by fish and plants in your tank.

But what if you have very soft water? Or maybe, you just want to increase the GH higher than what your tap water currently contains?

Well, that’s where the following come in…

2. Water remineralizer

RO/DI water is very soft water that has been stripped of all its mineral content. It contains zero GH and, on its own, is unsafe for fish and plants.

Remineralizer restores the lost minerals. But it’s not just great for RO/DI water, you can use it to raise the GH of soft well water or tap water as well!My favorite remineralizer is… Aquasana Remineralizer.

Aquasana AQ-RO3-RM Replacement Remineralizer for OptimH20 Reverse Osmosis Water Filter,White
  • Genuine replacement Remineralizer for Aquasana OptimH20 Reverse Osmosis Water Filter: AQ-RO-3
  • Use only genuine Aquasana replacements – untested replacements are not certified for performance capacity or contaminant removal
  • Replacements made easy – no tools or plumber required – replace membrane every 12 months

By following the included instructions, this remineralizer allows you to reach a specific GH with little effort.

Seachem Replenish contains sodium chloride, so it is not suited for planted tanks or salt-sensitive fish, such as certain breeds of catfish.[7]

Fortunately, Seachem makes a remineralizer that is safe for plants and salt-sensitive fish too…

Seachem Equilibrium 600gram
  • MINERALS: Equilibrium is specifically designed to establish the optimal mineral content for the planted aquarium. When this mixture is added to the aquarium it will impart a slight haze that should clear within 15–30 minutes.
  • EQUILIBRIUM: Does not contain sodium or chloride (which can be detrimental to a planted aquarium at elevated levels).
  • SUITED FOR: Equilibrium is preferably suited for use with RO (reverse osmosis) and DI (deionized) water or any mineral deficient water.

Free from sodium chloride, it’s perfect for raising the GH in your planted tank.

Remineralizer is generally added each time you perform a water change.

3. Wonder shells

Weco Wonder Shell Natural Minerals (3 Pack), Small
  • Made of natural materials
  • Removes chlorine instantly
  • Clears water

Wonder shells contain magnesium and calcium. When added to your aquarium, these shells slowly dissolve, releasing these elements into your aquarium and raising your GH.

Wonder shells also condition your water, removing chlorine and chloramine from tap water and can help reduce cloudiness as well. They are particularly popular in small beginner aquariums.

Just be mindful that it will take some trial and error before you know how many shells you need to reach a specific GH in your tank.

4. Crushed coral

Crushed coral used to raise general hardness (GH) in aquarium

Crushed coral is exactly what it sounds like. Coral that has been harvested from dead reefs.

Because coral is largely calcium carbonate, it slowly releases calcium and carbonate into your water when added to your tank.

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

Carib Sea ACS00120 Crushed Coral for Aquarium, 15-Pound
  • 100%aragonite supports proper ph
  • grain size reduces built up detritus
  • re-create natural reef environments

The one thing to be mindful about crushed coral is that it will raise not only your GH but also your KH. The higher KH means that your pH will also be higher.

It’s these exact characteristics that make crushed coral a popular choice in cichlid tanks, which prefer hard water with a high pH.

5. Aragonite

Crushed aragonite used to raise general hardness (GH) in aquarium

Aragonite is available as rocks or sand. Like crushed coral, it is made up almost entirely of calcium carbonate. When added to your aquarium, it releases both calcium and carbonate into your water.

Aragonite is mostly used as a substrate for hardwater-loving fish like African cichlids. It’s more pleasing to the eye than crushed coral. You might also hear aragonite sand referred to as cichlid sand.

Just like crushed coral, adding aragonite to your tank will not only increase your GH but your KH and pH too.

Some brands mix both aragonite and crushed coral together in one product to make it more visually appealing.

How to lower aquarium GH – decrease hardness

Okay, so decreasing the GH is slightly more difficult than increasing it. If you have hard water, you may find it easier to keep hardwater fish than plants.

Let’s take a closer look at the different ways to lower the GH of your tank.

1. Reverse Osmosis/Deionized water (RO/DI)

RO/DI unit to create pure water for aquariums

If you need to lower your GH every time you perform a water change, an RO/DI system is your best bet.

To put it super simply, this device removes salts, minerals and other contaminants leaving you with 99% pure water.

Best of all, this water is soft. So soft, it has a GH of zero.

So with your RO/DI water on hand, you have two choices:

1. Remineralize – Start from scratch and raise the GH to your desired level using a remineralizer like Seachem Replenish.

2. Dilute – Use the RO/DI water to dilute your tap water, lowering the GH down to your preferred level.

While it may be expensive to set up initially, an RO/DI system saves you money in the long run.

The other option is to buy bottles of…

2. Distilled water

Bottles of distilled water

Distilled water is essentially water that has been turned into steam then collected. When water turns to steam, it leaves behind salts and minerals, resulting in pure water.

Like RO/DI water, distilled water is soft and has a GH of zero and cannot be used on its own. It must either be remineralized or mixed with your tap water to increase the GH.

3. Peat moss

Two hands holding peat moss used to lower general hardness (GH) in aquariums

Peat is dried and chopped up sphagnum moss and, when added to your tank, can be used to soften your water.

Simply add peat to a mesh bag and place it inside your filter. As the water passes through the peat, it traps the GH minerals like calcium and magnesium. By removing and replacing the peat, you remove these minerals and soften your water.

There are some downsides to using peat. Namely, it’s not a very precise method of lowering GH, and its impact can be virtually unnoticeable on hard water with a high GH.

Peat also releases tannins, which can lower your KH and pH as well. These tannins also dye your water a yellow color. Depending on what you stock, this may not be desired.

Some people use Indian almond leaves to similar effect.


For those with soft or hard water, understanding and adjusting GH is an important part of fishkeeping.

While many beginners get by without testing their GH at all, there is a good reason why you should – the health of your fish are at stake!

Besides, as you see from this article, testing, raising and lowering the GH of your tank isn’t that difficult anyway.

Do you test your tank’s GH levels? Let me know in the comments below!

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 (61)

Thank you for your time in putting together such a well written, comprehensive guide.
In reviewing this resource I thought that I had seen mention of columnaris but now can not locate it. Can you confirm?

Hi Ian,
I use RO/DI water in my community tank but I’ve noticed that my GH has gradually risen over time.
When I do a water change I set the GH in my RO water using Seachem Equilibrium to my desired level of 8dGH and add that to my tank.
Would I be better off testing my tank and adjusting my GH in my RO water accordingly or continue to set it to a predetermined level ?

Many Thanks

Hi Derry,

Generally when dosing with additives, it’s best to test the tank and use those results to determine the dose. Blindly adding a preset amount of anything can certainly lead to issues. Lucky for you, this is an easy fix 🙂 Much of fishkeeping is a balancing act!


I would appreciate your guidance on lowering the pH in my new 40 gallon aquarium. It is at 8.4. I need to transfer my very large common goldfish from a 20 gallon, pH 7.2. I have tried for several weeks with water changes but need to be more aggressive. I have a whole house water softener because I have well water but the pH is still very high.

Hi Michael,

I can provide advice relative to articles on my site. It’s nothing personal. I no longer provide generalized advice as I was spending over three hours each day replying to comments. I wish it wasn’t the case but between my 9-5 job, my family and my fish, I don’t have that much time. If you need step by step help, I highly recommend joining an online aquarium forum like these ones many experts hang out there and love to provide help!

Yes and it never turns green starts out clear turns yellow my kh is 2 drops can I lower the gh raise the kh ?. My ph starts at 6.4 from tap goes up to 7.2

No, lowering the GH will not raise the KH. Something in your tank is responsible for raising the pH of your water, possibly something leaching.

I test my water every week when doing water changes. My location (also water parameters) and tanks are newly setup. My town tap water comes out like R.O. water with a touch of chlorine. I raise my GH with Seachem’s Equilibrium to 5 dGH and my angel fish and guppies are breeding fine and are healthy. My live plants are all doing good too.

My taps KH is also zero and pH is 6.0. I raise both by adding sodium bicarbonate until my pH is 6.8. My KH ends up fine too and my pH doesn’t fluctuate.

Just need to find a cheaper alternative to Equilibrium, It goes fast when working with 22 tanks!

Hi Jim,

Wow, 22 tanks? That sounds like quite a fish room. My 4 tanks keep me busy enough and is a compromise with my wife. If I had my way every corner of my home would be filled with them.

That’s sure is some soft water you are dealing with. Lucky you have Sodium Bicarbonate, it’s considerably cheaper than Equilibrium! I can’t think of a good solution here short of moving to a new location with harder water. And I shudder to think at the logistics involved in moving 22 tanks.

GH booster is a mixture of salts (often not including NaCl), for example “Barr’s GH Booster does not contain Iron, just 3 parts K2SO4, 3 parts CaSO4 and 1 part MgSO4.” acording to a forum post on the topic.

You can make your own GH booster by purchasing these extremely cheep chemicals and mixing them yourself. MgSO4 is just epsom salt, CaSO4 is just plaster of paris, K2SO4 is not commonly used in the household but is sometimes used as a road de-icer and is actually a form of waste from the chemical industry.

I am aware you posted this more than a year ago, but i hope this helps you or someone in a similar situation.

My source of water is a well. It is quite hard with significant iron so I am running an iron filter followed by a water softener using NaCl. I have been using the softened water in my 55 gal freshwater, planted tank. Do these tests for GH detect the Na+ ion from the water softener? What about the KH test? I would guess it depends on the specific indicator. The tap reads about 120 ppm on both, pH 7.5-8. What is your recommendation? I don’t really want to explain to my wife why we need an RO system if I don’t have to. Feel free to be as technical as you want, I can handle anything you can throw at me. Thanks for any help.

Hi John,

A KH testshouldn’t pick it up, it’ just detects CaCO3 I’m going off my experience of using API test kits here. A GH test kit will detect CaC03 as well as other minerals, like Na. Test kits are not that good at creating a complete picture. Ideally you want to know the basic composition of your water and then use test kits to look for clues that something is amiss. For those on tap water, there are very few surprises. For well water, I would use an ICP-OES test there are pre-made kits available on amazon and at local fish stores. Basically, take a sample of your water and send it away to a Lab. If you do go down this route, I recommend the ATI one. It might be sent over to Germany, but the last time I checked, it had tests that competing labs in America didn’t offer.

Unfortunately, I personally do not have any experience with using water softened water. However, given that you are essentially swapping out calcium with sodium, It could be problematic for freshwater fish. Some are more tolerant than others, but ultimately it should mostly be avoided.

Hi Ian, my newly set up is a 40 gallons planted aquarium. For substrate I used organic soil caped with black blasting sand. To do water change I use RO and Eqillibrium when tested GH aquarium is 25 + degree. Do you have any idea what make GH increase. Thanks you

Hi Dao,

Unfortunately there isn’t enough information to go off here to narrow down the cause of your KH spike. If the levels are going up, continuously, then something you are adding or have added to your tank is responsible. Unfortunately, it’s often a case of removing a possible cause piece by piece until you Identify what was responsible.

Hi sir ian. I have an important question. I lived at the coastal in philippines and i have been culturing mudcrabs in ponds. I mixed saltwater and deepwell water and achieve a salinity of 1.5, kh of 13dkh, ph7.29, and calcium at 280ppm. I used hydrayed lime diluted to increase ph,kh, and ca. After days of trial. I increase my kh to 14, and ph8.2 but my ca at 300ppm. How can i achieve 500pm of ca? Maybe i diluted my hyrated lime wrong as ca precipitates. Any advice on how to stop ca precipitation or other ways to increase my ca

Hi Mark,

Unfortunately, ponds and the conditions you face are well out of my area of expertise. Do you have a local forum or group of people that do something similar? They would be the best people to go to for advice.

I have a neo shrimp tank with small rainbow fish . Live plants, driftwood, mineral rocks, mineral balls, sponge filter and ziss filter.
Ammonia= 0 nitrate=0 nitrate=20 Kh I had to put in 3 drops in test tube (not sure what it means) Gh I had to put 11 drops in test tube (not sure what it means either). Does this all sound ok or am I needing to change something?

Hi Sharon,

Unfortunately, you’ll need to relate your test kit back to the preferred kh of your tank critters. The instructions on the KG and GH test kits should outline clearly what the amount of drops means and give you an explanation of how to convert that to ppm.

On the ammonia, nitrite and nitrate front, it all sounds fine, as long as you are performing your weekly water changes.

Hello! I just discovered your website, so I hope you’re still working on it and blogging! I wanted fish for years, so I ventured out…but didn’t do the volume of research on them, the way I should have! I got my fish in January and WOW, they are all STILL ALIVE!! These poor guys have been on my end of trial and error…and believe me when I say, I have LOST SLEEP over the thought of being responsible for them dying! I have dug & dug to learn as much as possible, correcting any and all mistake made…and again, they are ALL still alive and doing good. My only heart break is the one gorgeous Betta I have, has some shredded fins, I think from the stress when I first got him. Anyway, I’m still learning SO much and sometimes think I’ve bit off more than I can chew…I had NO idea fish could be SO complicated! One Betta is in a 5-gallon filtered tank alone…my other 5-gallon tank has one Betta and 2 guppies, who all get along great…that Betta is VERY easy going, LOL!! Long story of how I ended up with 2 tanks…another error I made buying 2 male Betta’s, not knowing they’d kill each other in the same tank. My question to you, if you get this message is….on those API 5-in-1 Test Strips, what do the numbers mean on the chart???? I’ve never used them, but bought them to get a small idea of what my chemical balances are and for my GH it’s 30 for my KH it’s 40. But what does 30 & 40 mean??? I do water changes once a week…and I now no longer change the filter…another thing I learned NOT to do. Amazing these fish are still alive…did I say that already, LOL!! People I’ve spoke with who have Betta’s laugh at me putting them in a filtered 5-gallon tank…they think a vase with Bamboo is sufficient…how truly ignorant people are. If you could help me with the GH and KH numbers I would really appreciate it and would it be possible to ask questions, in case I have them along the way?? I want to master my tanks and eventually get a huge aquarium for my home….but only when I know exactly what I’m doing!! Thank you for your time and attention! Debbie

Hi Debbie,

Welcome to the world of fishkeeping, there is a lot to take in but don’t worry, it gets much easier – it always surprises newcomers that fish are so much harder to keep than dogs or cats which is interesting as many people think of them as “beginner” pets.

When your test strips run out, I highly recommend using an aquarium test kit instead. Not only are they more accurate, but more affordable too – one kit can last years. The API master test kit has everything you’ll need.

So in the United States, most people don’t have to worry about KH an GH unless they have very soft or very hard water. Based on your readings, you probably don’t need to keep checking them – your mineral content is good enough for a single betta that you can replenish these trace minerals with your weekly water change.

Your most important parameters that you should watch weekly will be:

Ammonia – I don’t believe API test strips cover this, but it’s super important it’s kept at zero. Raised levels of ammonia can be responsible for fin rot

Nitrite – Another toxic one that you want to keep at zero.

Nitrates – These will forever keep increasing. Part of the reason for your weekly water change is to get these back down. In a non-planted tank you would aim to get it down under 10 with your weekly water change. Ideally you wouldn’t want it to exceed 40

I’m fine with you asking questions, but they will need to relate to an article on the site (ask in the comments there) unfortunately, I cannot give 1 on 1 advice. I used to, but I was soon spending up to 4 hours a day typing out replies. As much as I would love to, if I do it for you, it would be unfair that I don’t do it for everyone. I hardly have the time to update this blog as it is.

Your best friend in fishkeeping will be a good local fish store (not petco or petsmart) they should use the same or similar water source to you and will be best situated to answer any questions or concerns.

Thanks for the helpful article. I live in a very hard water area and am planning on using demineralised water with Seachem Equilibrium for my axolotls. From my research, axolotls require moderately-hard water ranging from 7–14 degrees of hardness. This might be worth putting in your table 🙂

Hi Hannah,

That’s very interesting. Being a fish kinda guy, I don’t have a whole lot of experience with Axolotls, but I can see how that would be useful info. I have added it to the table. Thank you so much for sharing!

I started a 10 gallon tank for my son about 2 months ago and it went great and cycled fine. Clear as can be. So I decided to break out my old 30g tank and give him a larger aquarium. I cleaned the new gravel and transferred the old tank water and fish to the new tank along with the old filter in conjunction with the new filter and treated water that was allowed to sit for 5 days. Within a week the water was milky white. The Gh is the only parameter that was high. I did a 15% water change with no visible difference. I treated for bacteria bloom with no affect. I then did a 6 gallon change with distilled water and the Gh seems to be higher like off the dip strip high! What could it be? The rocks are all I can think of and they were purchased at Psmart and are name brand. Is there anything I can do other than drain the tank and remove the rocks??


Hi CT Ford,

I’d avoid using the dip strips as these can be wildly inaccurate. Your best bet would be buying an API master test kit, then there KH+GH test kit separately, to confirm your results. It’s really difficult to make an informed decision without knowing for sure what your water quality is. From here, it should be much easier to give advice on how to proceed.

I used the API kit to measure my 30 gallon fresh water aquarium and got the highest (180) GH; 0 KH and 200 NO3. Various fishies died although still some live and seem to be ok.
Could someone help me balancing these as needed to maintain healthy fish?

Hi Vero, it sounds like you need to spend some time doing water changes and reading up on aquarium maintenance – that level of nitrate is way too high.

Hi Ian

Really enjoyed the above article – this is an area that I’m struggling with. I was advised by my local fish shop not to worry about water hardness, but after my third dwarf gourami died I did some investigating. My water quality is fine but – after using the API test kit on gh and kh I think I have a problem – the KH is 11 (and then 9 after a water change) and the GH is 13 – I tested twice to make sure (before and after a water change). Ph looks to be 7.5. I have fish that need softer water – neon tetras, shrimp and a honey gourami. I can’t get RO water each week and can’t afford to buy a unit. It’s a small tank at 60 litres with an internal filter. I’m actually planning on starting a bigger tank soon so definitely need to work this out. I’ve ordered some alder cones and oak leaves but can see this won’t help much and I have bog wood already in the tank. It’s heavily planted too. Any advice would be appreciated- wish I’d known about this before – maybe I’m better off with cichlids?

Many thanks

Hi Sam,

That is some hard water you are dealing with. I know it’s probably not what you want to hear, but for the easiest and least expensive maintenance, my recommendation is to buy fish that suit the water that comes out of your tap. RO units, KH/pH adjusters etc, are all an ongoing cost and come with extra effort. Same goes for people with softer water who want to keep hard water fish. This isn’t a bad thing, you have some stunning hard water fish to choose from.

Thanks Ian. I still have the issue that my existing tank has fish in it that want softer water – I’m quite happy to try and alter the water chemically during water changes – I change about 11 litres a week. Strangely the ghost shrimp seem to be thriving in this tank. If I did go down this road how would you recommend I do it? I’ve been looking at Seacham acidity buffer – but they also say I need alkaline buffer too (not sure I need that!). With the new tank, which fish would you recommend I look at? I feel like my water is in an awkward place – not soft enough for community/soft water fish and not hard enough for fish that prefer hard water (general parameters seem to be 12-20).

Thank you!

If you go down this road, buffers are probably the easiest and consistent way to do it. If your water is hard, you may be able to get by with Neutral Regulator, by seachem, which drops the pH to 7 and keeps it there. If you are going this route, you’ll need to constantly monitor your pH and KH levels for swings in the early stages, until you get a sense of how much of each product to add and how it works – it can be a bit of a balancing act.

They’ll likely recommend you need the acidity buffer an alkaline buffer as pH and KH work hand in hand. If you are going to mess with the pH, I highly recommend checking out this article on KH

It should explain the idea quite simply.

Thank you so much for this very informative article. You have probably just solved the problem as to why my fish are stressed each summer. I usually exchange approximately 1/3 of the water at at a time and in the cooler months all is well. In the summer I remove the same amount and then top up whatever has evaporated, so presumably the GH is rising each time I do that (currently 18-20 – I only just checked it after being very frustrated that pH is fine at 8, nitirites are negative and the fish are still stressed….) Have you any advice as to how much extra water I should remove at each exchange in the summer? The GH of the tap water is OK (around 8)

Hi Beth,

This is a difficult one since you’ll have to find the balancing act through trial and error yourself. Generally, if you are performing a weekly water change of 30-50% GH continuing to rise shouldn’t be an issue. If you do it less, and top up instead, then it can cause GH to climb.

However, I must add that it is very rare that I have seen GH be the cause of stress in fish. What behaviors do they exhibit to show stress? Also, is their tank getting too warm in summer? This can be a major issue for cold water fish in hot climates.

Hello Ian, my name is Lisa and I wanted to ask a few questions on my tanks GH, I am a member of a few fish sites online like on Facebook goldfish keepers and a few others. I wanted to ask everything was fine and my tank the ammonia with zero nitrite 0, and nitrates 10/20 I never let them go much higher than that . Anyway the apartment but I moved into has soft water it’s well water but they have a softener on it, the pH is about 7.5 I test it with a pH probe, I also have the APL liquid test kits, my Gh in my tank was 17.9 and my kh was at 143.2 put my fish we’re getting a lethargic, and not looking healthy, so I tested the water , and scene that’s the GH was really low , now I did go to the my flashlights and ask for help on the GH and they told me that it didn’t matter that it was so low and not to change it, but my fish were not improving and I could not find out anything else that was going on in my tank, I did not change anything , I haven’t lived here that long so I went from really good water at my other house and then I moved and now this , I’ve been using equilibrium made bye seachem, and it is helping , to bring it up, but wanted to ask if I was doing the right thing by bringing it up when some people told me not too, I read that goldfish need a GH of up to 150 to 200, but others say it doesn’t matter , I also have plants in my tank that would always die , and now they also are doing better with me adding the equilibrium, I just wanted to know if I was doing the right thing or not I have 75 gallon tank 3 fancy tail orandas goldfish that I’ve have had for years , and I have never had any problems with them before , I also do my water change every week faithfully my fish are large so I do 35 gallons in a 75 gallon tank each week, and before I do my water change I checked in nitrates set my water changes are based on how high my nitrates are I do not let them go very high I like to keep them around 10 PPM now higher than 20 ppm, I have sand substrate I also have an FX4 on there with a306 fluval canister filters, I don’t know what else to do I don’t know where else to add and I don’t even know I’m doing the right thing I think I am because it’s working, also I was worried about what other people had said, most people tell me don’t worry about the GH in the tank that it didn’t matter just worried about the KH in the pH, so this is why I am so confused, if you can help you answer my questions would be very much appreciated thank you Lisa

Hi Lisa,

If your water is incredibly soft, then it can mess with the osmoregulation of fish. Some hardness is essential. I guess the big test will be that if your fish improve on the back of using equilibrium alone. If they don’t then it’s possible that something else is at play.

Drift wood also lowers gh right? Why didn’t you add that point?

Also you should mention any small amount of ammonia, nitrite and nitrate are deadly to fish living in high ph/gh water than the fish living in low ph/gh water.. This is so important to know…

HI Karthickeyan,

This is entirely driftwood dependent. Not all wood leaches tannins to the same degree, which is largely responsible for the lowered ph/gh. It’s also not a good solution since you can not control the amount the driftwood leeches. To say “drift wood lowers gh” isn’t entirely helpful to the beginners this guide is aimed at without complicating what is already a confusing subject.

Hey! Want to start with discus fish, but the Gh in my aquarium is 5… Is that good for diacus? Or should it be lower. Other things I can do to get the Gh lower? Thanks..

Hi Fishlover,

It sounds like you should read up on discus and their preferred parameters if you are asking a question like this. Googling “discuss care sheet” will help.

It depends on your source, are they tank bred or wild imports? Tank bred, ask the breeder what his water parameters are.

There are many ways to naturally lower the harness if you really think 5 dh is to high (I don’t think it is). Peat moss, catapa leaves, driftwood, many more… Google can sometimes be your friend.

Having tested our water today our total hardness is >21, carbonate hardness is 20, pH 8. We live in a very hard water area. Our tank is fresh water and planted. We have tropical fish and a temperature of 24 degrees. We have lost 5 of our 7 cardinal tetras over the last few weeks. Nitrite and nitrate levels are within the acceptable range. Do we need to do anything about our GH level please and if so, what?

Thank you

Hi Susanne,

>21 DGH is too hard for Tetra. The PH is too high as well. The fact that you say nitrite is within the acceptable range has me concerned as well, since the acceptable reading for nitrite in a cycled tank is zero if you are reading any nitrite, then it’s a clue you may need to cycle your tank.

I have a 550 gallon in wall Frontosa tank. I’m finishing out my fish room behind this tank and have a continuous water change drip setup. Total system volume is 750 gallons and will be increased to 1100 or so with my new tanks.
My tap water is very hard with a GH of 19-21 and a KH of 16. It has a lot of dissolved Co2 so the pH out of the tap is 7-7.5. It raises to 8.8-9.0 after aeration.

My problem is mineral precipitation. I notice if I run straight tap through a carbon block filter I will get cloudy water and my filters will clog with minerals fairly quickly.

I’ve done both larger periodic water changes and continuous drip with same result. Only advantage of periodic large changes is it clears up after a couple days but it’s inconvenient. Advantage of my drip is stability and less labor.

Currently I’m cutting my drip water with softened water from a whole house softener using two needle valves at a ratio of 1:3 soft to hard. I Know this is not ideal but seemed to reduce the precipitation to almost non detectable but my tanks GH has dropped to 9 from 12-14. Getting it dialed in has been a challenge.

I’m having trouble finding a good solution. I’d love to just use my hard tap water without dilution. It’s perfect really. Would having my tap water flow through a water tank with good aeration help maybe stabilize this drip system? It would solve two issues, bring the temp up, remove the dissolved CO2, match tank pH etc… not sure if the minerals would precipitate in this tank and maybe get filtered out before going into the tank?

Any advice would be appreciated on dealing with my liquid concrete tap water.

Hi Jeff,

That IS some hard water. I think you are correct on the holding tank approach but I don’t see a method of reducing hardness without diluting it. I think that even with good aeration, you’ll have the same problems.

Hi Ian,

I’ve been keeping fish for a number of years in rock hard high ph water (26dkh, 22dgh and 8.7 ph at time of writing). Although this is dramatically higher than most fish should be in, I have had no problems keeping many species and even breeding some in these conditions.

Assuming the fish are properly drip acclimated to these parameters, do you expect the overall life span of the fish to be reduced? I’m considering cutting tap water with 2 parts RO for the overall health of the tank, but this adds an additional level of complexity and there isn’t really an immediate gain from this since I’m not keeping any notoriously sensitive fish in this particular tank. With it being heavily planted, it’s nice to know I can skip some occasional water changes and not worry about nitrates or ph crashes.

Interested in your thoughts on this.

Hi Dustin,

To be honest, it entirely depends on the fish. While care guides often list a recommended kh/gh, many fish can tolerate or live seemingly happy lives outside of these parameters. A lot of it has to do with sensitivity, which is a difficult thing to measure because you can have more or less sensitive fish within the same species. pH is generally the most important parameter to follow, but it goes without saying that a fish that can live in high pH will be fine with high gh/kh too given the interlinked relationship of the three.

At the end of the day, fish keeping is somewhat of an experiment hobby. That’s what makes it so fun. If you are seeing success and long lives, then keep doing what you are doing!

Ian good evening,
I have a problem that’s driving me crazy. We’ve had a recent change in water companies in my area and the water qualities change up and down and I’m constantly testing water.The problem is that we have a continually changing DGH and its always on the High side anywhere between 8-13 DGH. I have a planted aquarium, with fish that can survive between 6.6- 7.2 Range the problem here is I get a PH bounce I try to keep the Tank in a DKH range between 3.5 – 4.5. I’m also using DI water to try and make corrections along with Seachem products except for Neutral Regulator which has to much Phosphate. I’m also dosing with CO2 during the day and using Seachems Acid Buffers and Alkaline Buffers trying to keep this tank stable.I do 15to 20% water changes about every two weeks. I’ve had planted Aquariums for at least 20 years and have never had these type of problems that I couldn’t work through. I’m at a loss and frustrated. Any suggestions that you may have would really be appreciated.

Hi Mike,

That sounds like an absolute nightmare. Unfortunately my suggestion is to typically create a tank to suit the water out of the tank. This way you are not reliant on balancing the water and constantly buying buffers/regulators. Stablizing water is a lesson in frustration.

However, you already have a tank set up for a different type of water, and now have continually adjust it, to which I don’t have a satisfactory solution in addition to what you are already doing. Short of rehoming your current fish and starting anew, I can’t think of a viable option.

Hello Ian,
Great site, I learned a lot -Thanks!

Question about GH (in these times of pandemic and self-quarantine), I have a case of very hard water 16+ dGH. I would like to lower it. Is there a way to “near distill” water? I am trying to avoid going to any store.
What about boiling a large pot of water and letting it cool? won’t that make the minerals come out of solution? then use this for a minor water change – and so on.
I appreciate your advice!

Hi Jon,

Great question. Unfortunately, you have me stumped. Boiling the water wouldn’t work unless you are collecting the steam, that’s the purified bit. The minerals will stay behind in the solution. Can anyone else weigh in here?

thanks for answering questions, my mess is as some others is my gh has gone sky high, The tanks have been up for 3 years and i have never had this problem. I am very high risk with virus no way to go out. i can order but wont be able to touch for weeks, got any idea, i love the guys but cant rish my health. any info great. Stay Safe Always

i just did a cleaning 4 days ago. numbers were fine them, my other tanks have , hell i dont know whats happening.

Hi Mary,

I’m so sorry to hear about your unfortunate situation. If you are looking to cut your water with ro/di water to get the hardness down, then look into how to make distilled water at home. There are multiple ways to do this, but they are all a bit of a chore.

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