Last update: November 2, 2022

The best water conditioner for aquarium to make your tap water safe!

You can’t see it…

You can’t smell it…

Often, you can’t even taste it…

But this invisible assassin is an expert at killing your fish.

I am talking about disinfectants, like chlorine and chloramine, found in your tap water.

To you and me, these disinfectants are considered harmless.

But to your fish, they are deadly.

Want to use tap water in your aquarium?

If you don’t remove these disinfectants, your fish will die.

Fortunately, water conditioner is what you need to do exactly that!

Today, I am going to teach you everything you need to know about water conditioners.

What is water conditioner, and what does it do?

Bottle of water conditioner next to fish tank

When most people mention water conditioner, they are talking about a solution that you add to tap water to make it safe for your fish. It changes the condition of the water.

You see, the reason tap water is considered safe to drink is because it has chemicals added to it to kill bacteria and viruses.

The problem is, these chemicals not only kill your fish but also the good bacteria inside your aquarium – the ones providing biological filtration to your tank.

By adding a water conditioner to your tap water, you neutralize these chemicals, keeping your fish happy and healthy.

A quick history of aquarium water conditioner

The history of aquarium water conditioner

At first, the only disinfectant in tap water that aquarists needed to worry about was chlorine.

Chlorine was simple enough to get rid of – you could remove it by letting the water sit for an extended period of time or by simply boiling the water.

Then, along came a game changer: sodium thiosulfate.

When added to tap water, this compound instantly removed chlorine. Best of all, it was harmless to fish.

This could be considered the first water conditioner.

Then, the game changed again.

Water supplies began to add both chlorine and ammonia to the water. These two chemicals combine to form chloramine.

If you just remove the chlorine, you leave behind the ammonia, which is also dangerous to your fish.

And so a new water conditioner was introduced, one that not only removes the chlorine but also neutralizes the ammonia.

Today, water conditioners do so much more than just remove chlorine and neutralize ammonia…

They also remove metals like lead and copper, help get nitrates under control and even contain additives like aloe vera that can improve the slime coat of your fish.

Beginners and experts alike can simply add water conditioner to their tap water and neutralize all the nasty stuff.

Preparing water for aquariums has never been easier!

Do you need to use water conditioner?

Woman shrugging her shoulders while holding bottle of water conditioner

I am often asked:

Why can’t I just add straight tap water to my aquarium?

I usually answer this question with another question:

Do you think there are fish living in our municipal water supply?

The answer, no.

And that’s because the water contains so much chlorine that fish can’t live in it.

But don’t just take my word for it…

An observation published under FAQs of Duke University states that at higher concentration levels, chlorine can kill fish almost instantly[1]

It doesn’t take much chlorine to kill your fish.

Your tap water likely contains more than enough to do the job…

According to the World Health Organization, most drinking water contains concentrations of between 0.2-1 mg per liter of chlorine.[2]

Even on the lower end, that amount of chlorine is lethal to fish.

The Food and Agriculture Organization of the United Nations states that active chlorine concentrations of 0.04-0.2 mg per liter are considered toxic to the majority of fish species.[3]

Fish don’t swim in chlorine in their natural environment – so don’t add it to your tank.

Unless you really know what you are doing, I recommend using a water conditioner for tap water.

How often should you use water conditioner?

You should use a water conditioner every time you perform a water change or top off your freshwater tank.

Simply add the water conditioner to the tap water before you pour it into your aquarium.

If you don’t, you are basically dumping toxic chemicals into your fish tank.

Those of you who are in the process of cycling a new tank need to add water conditioner every day until your tank has finished cycling.

What are the different types of water conditioners?

Bottle of water conditioner viewed under magnifying glass

At the time of writing, there are four different types of water conditioners commonly used in aquariums.

1. Dechlorinator

Instantly removes chlorine but leaves ammonia and heavy metals.

Even though dechlorinators have become less popular because they do not deal with ammonia, you can still find them on pet store shelves. CrystalClear Vanish is one of the more popular brands.

Warning: If your tap water contains chloramine, a dechlorinator can cause ammonia to build up to dangerous levels!

2. Chloramine neutralizer

Instantly removes chlorine, breaks down chloramine and neutralizes ammonia in one of two ways:

  1. Binds the ammonia molecule, causing it to become harmless to your fish
  2. Converts the ammonia into ammonium, also harmless to your fish

Fritz Pro is a popular water conditioner that just focuses on chlorine and chloramine without all the extra stuff.

While some brands of chloramine neutralizer will also neutralize heavy metals, others will not – always check the packaging to make sure that you are buying the right water conditioner for your situation.

Important: If you use an ammonia test kit that is not specifically for ammonia (NH3), it can also pick up the harmless ammonium (NH4). This can make the result look dangerously high, even though it isn’t.

3. Complete conditioner

Generally speaking, when most aquarists mention water conditioner, this is the type they are referring to.

As the name suggests, this water conditioner does it all:

  • Eliminates chlorine
  • Neutralizes ammonia
  • Detoxifies heavy metals
  • Eliminates copper
  • Buffers pH
  • Protects fish slime coats

And more…

The number of actions entirely depends on the brand of complete conditioner.

My personal favorite complete conditioner is Seachem Prime. I use it in all my aquariums, and it takes the top spot in my best water conditioner recommendations.

4. Reverse osmosis water conditioner

Okay, so technically this isn’t a water conditioner but rather a re-mineralizer. But because both manufacturers and hobbyists refer to it as a water conditioner, I decided to include it.

Many reverse osmosis (RO) systems remove chlorine, chloramine and the other nasties found in tap water.

Because of this, you won’t need to use a water conditioner with RO water.

But RO water also removes the good stuff too, like calcium, potassium, sodium and magnesium – trace elements that are essential for a healthy tank.

An RO water conditioner replaces these missing minerals.

Why shouldn’t you use water conditioner with a saltwater tank?

Don't use water conditioner in a saltwater aquarium or reef tank

Water conditioner should be used with freshwater aquariums only.

This is because water conditioner does not remove chloramine and heavy metals. Instead it neutralizes them, rendering them harmless to your fish.

The problem here is that they still exist in the water, meaning algae and cyanobacteria can still use them as a food source.[4]

Where possible, I recommend using reverse osmosis/deionization (RO/DI) water for saltwater aquariums – which does not have the same problem.

That said, a bottle of water conditioner can be a life-saver in an emergency where you find yourself needing to treat tap water for your tank. I keep a bottle on hand, just in case.

One final word of warning for those of you with protein skimmers – unless a water conditioner specifically states that it won’t cause a protein skimmer to foam, I would recommend caution.

When in doubt, assume that your water conditioner is not protein skimmer safe.

Using water conditioner with a small tank

A little bit of water conditioner goes a long way.

For smaller tanks, like betta tanks under 20 gallons, it can be difficult to measure out a precise amount with the cap. Often you only need a couple of drops.

That’s why I use a measuring syringe like this one.

It allows me to accurately measure out even the smallest amount so that I don’t add too much water conditioner to my tank.

The best water conditioner

Best water conditioner sitting on top of winner's podium

I was considering making a list of the most popular water conditioners. But when I stopped to think about it, they all do a similar job to varying degrees of success.

But one water conditioner is unrivaled in its ease of use, ability to condition water and value for money. When it comes down to it, I honestly can’t recommend anything else…

The best water conditioner – Seachem Prime

Seachem prime best concentrated water conditioner for marine and freshwater tanks

Fast facts:

  • Long lasting – 500 ml treats up to 5,000 gallons (20,000 liters)
  • Does not affect pH levels
  • Removes chlorine, chloramine
  • Detoxifies ammonia, nitrates, nitrites
  • Detoxifies heavy metals
  • Encourages natural slime coat in fish

If you use a water conditioner with your aquarium, then you are likely nodding along at my top pick. As a water conditioner, Seachem Prime is unbeatable.

Ask any aquarist to recommend a good water conditioner, and Seachem Prime will likely be the response.

Not only is Seachem Prime a complete conditioner, but I found that it lasts the longest. It was the most concentrated formula on the market, meaning you don’t need to add as much to your water.

A bottle of Seachem Prime can last years depending on the size of your tank, and with no expiration date, it won’t go bad.

Seachem Prime is also protein skimmer-safe.

Seachem makes a similar water conditioner designed just for reef tanks, Tetra AquaSafe Plus. While you can find it online occasionally, it is typically only stocked by local fish stores. While I recommend using RO/DI water for your reef tank, I keep a bottle on hand in case of emergency.

Seachem Prime really is the ultimate aquarium water conditioner!

Seachem Prime Instructions (click to expand)

Use 1 capful (5 mL) for each 200 L (50 US gallons) of new water. For smaller volumes, please note each cap thread is approximately 1 mL. It may be added to the aquarium directly, but it’s better if added to the new water first. If adding directly to the aquarium, base the dose on aquarium volume. Sulfur odor is normal. For exceptionally high chloramine concentrations, a double dose may be used safely. To detoxify nitrite in an emergency, up to five times the normal dose may be used. If the temperature is >30°C (86°F) and chlorine or ammonia levels are low, use a half dose.


When used correctly, water conditioner is an effective way to make your tap water aquarium safe.

Water conditioner has become an essential part of my water changing routine.

One final word of warning before I end: Some brands of water conditioner smell like rotten eggs (sulfur). This is completely normal. Just do what I do and hold your breath when you measure it into the water.

Do you use a water conditioner for your aquarium? 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 (47)

Hi Arthur,

I do not have any experience using Weco Dechlor. However, one of our writers uses it in her discus tank and her fish are both happy and healthy.

I’m currently using purified water in my aquariums. Since it’s not necessary to use prime, what can I add to the water to benefit my fish?
Thank You

Hi Audrey,

While purified water (such as RO water) is free from chlorine and chloramine, it is also free from trace elements essential for osmoregulation and hardness which will prevent pH swings.

The process of adding a product to increase these elements is called remineralization. There are many products available to remineralize your water, such as
Seachem Replenish.

Hi Stephanie,

It depends on the water conditioner. For instance, you can use up to 5 times the recommended dosage of seachem prime (although this should only be done in emergencies.)

However, like with any chemical, it’s best to follow the instructions when adding water conditioner to your tank. But I wouldn’t be too concerned if you add a few drops extra by mistake.

I’m new to this. Is aqua safe okay for conditioning the water? I know everyone has certain ones they like to use.

Hi Ashely,

Plenty of people safely use Tetra AquaSafe to dechlorinate their water. But some water supplies also contain ammonia and nitrate. Aquasafe will not treat these. Also, because Seachem Prime is ultra concentrated, a bottle lasts a lot longer, which will end up saving you money.

AquaSafe = 1 teaspoon (5 ml) per 10 gallons

Seachem prime = 1 teaspoon (5 ml) per 50 gallons

You’ll go through a bottle of AquaSafe much quicker.

Hi, thanks for this great info. I just started to use Prime in my 200 lt tank. I do partial water change per week. I have a 40 liter bucket to do this. My question is, sometimes i dont have time to let the tap water sit in my 40 liter tank, like 24 hours or more, can i add prime directly to this bucket, after i fill it from tap? And can i make the water change immediately?

Hi Yucelene,

I’m not sure why you are waiting 24 hours. Prime neutralizes ammonia and nitrites for 24-48 hours – long enough for your beneficial bacteria in your filter to break it down.

If you are waiting 24 hours, you are essentially giving the prime an chance to wear off, which kinda defeats the purpose of adding it.

The whole purpose of water conditioner is to dose your replacement water then add it immediately to your tank – it really makes fishkeeping easier.

Hi Saeb,

With water conditioner so readily available, and with it being able to be used in an emergency, such as an ammonia spike, and with Vitamin c (ascorbic acid) costing more per use, I see no reason why vitamin C should be used instead.

In the article it says to add in conditioner to tap water before adding to the tank, but what if you are using the Python water changer that fills the tank directly from the sink? I’ve seen on amazon that people say to use the conditioner while filling but wouldn’t that still subject the fish to the toxins while the conditioner is working?

Hi Kevin,

Excellent question! In the case of using a water change system, you add it right before the water is added. The conditioning process is near instant. It’s possible this system does place more stress on the fish, but all tanks I have seen, my own included, do this method have had their fish reach the average life expectancy. Just make sure you dose enough for the whole tank, not just the water already inside.

Thank you so much
But they say that sulfur in the chlorine remover harms living organisms
As for the price
Our prices are quite the opposite .. Vitamin c (ascorbic acid) is equal in (price with the Primer Seachem) and cheaper as well.
Vitamin C is a fish helper as a treatment for wounds
What do you think؟

Hi Msaebr,

I have no experience with using Vitamin C and cannot comment on it’s efficiency. I wish I could help you more here. I would try posting on an online forum so can learn from others who have used it.

A friend of mine has just started doing community fish. She moved to a different apartment and all but two of her fish died I checked her water for her the tap water PH is at 8.3 so I got her to using prime but the PH can’t get it to come down nor the nitrates are between 40 & 80 she has a 38 gal tank what do you suggest how much prime can be used I put 5 ml . Please advise thank you

Hi Irene,

It’s possible that when she moved, the cycle crashed. If this is the case,t he tank would need to be re-cycled. Depending on how long it’s been, this might have happened already, on it’s own. On the pH level, prime isn’t going to do anything to reduce pH. If 8.3 is well out of your fishes comfort zone, then you’ll want to use a product to both lower and stabalize pH. Seachem’s Neutral Regulator is a popular product and easy to use product that will achieve this. Nitrates are reduced with water changes, you might need a few back to back water changes to get it back below 10.

From here you’ll want to monitor your tank, observing what happens and making adjustments accordingly.

Hi, Im new to all this been reading a lot now I have too much on my head.

What do you recommend to be used with Prime, Add Seachem Stability on a weekly basic?

Should I add also Seachem Stressguard? If yes how often once a month or once every two months?

Also if I only have space after the filter to use Seachem Matrix or Seachem Purigen which one should I use?

Thank you,


Hi Joel,

Unfortunately, there are no black and white answers here. It all depends what’s in your tank and what your test kit results return. Generally speaking, besides water conditioner, you should only add chemicals to counter an imbalance in your tank. This means that anything I recommend here may not be relevant to your tank.

As for the filter media, as seachem matrix and seachem purigen are vastly different products. One is for biological filtration (essential) the other is for chemical filtration (non-essential). If you don’t understand the difference between these two, then I recommend should either continue researching or go to your local fish store (not a big box chain) where an expert can step you through the process.

Hi Ian,

When i do water change for my aquarium, i use aged water. I age water 3 to 4 days in a drum with an air stone. Do i still need put or mix water conditioner in my aged water? And do i need to add little bit of salt when aging water for a freshwater fish like Arowanas and plecos. Thank you in advance for replying.


Hi Chris,

If your water contains chloramine, then yes, you do. Aging may not necessarily remove all of the chemicals that can harm fish.

Hi Ian,

Which process is better or should be:
1) After a 30% water change, i should put or mix the water conditioner in the aquarium tank.


2) I will put or mix the water conditioner in the drum where i age the water.


3) I will put or mix the water conditioner in the aged water before water change.



Hi Christopher,

Ideally, 2 or 3. You would only do 1 if you are using an aquarium water changer and have nowhere else to add the water.

The link to your recommended syringe dropper links to another de-chlorinator. Can you tell me which dropper you recommend? I have a 2.5G tank. thx!

Hi Matt,

Oh, you won’t need much seachem prime at all for that! I’ll have to fix this article at some point when I get the time. Thanks so much for pointing out the broken link. If you are just looking for a cheap solution, those plastic pipettes from amazon can easily measure out a ml. If you rinse them, you can get a few uses out of each before disposing of them. They are affordable as well. I now use glass ones, but they are more delicate, but they are less wasteful.

Hi Norma,

Follow the instructions on your specific water conditioner. You’ll have to remember that decorations and gravel displace some water so you may have to guess. Fortunately, many water conditioners are fine with overdosing to an extent. Seachem prime, for instance is considered safe up to a 5x dose.

Your comment is awaiting moderation.

Hello I’ve been reading you’re responding answers, I was wondering if you’re able to help with my issues, I cannot get rid of this ammonia in my tank n it’s driving me mad, my wife says I’m getting obsessed. I respond with no I’m passionate very passionate!!! Lol …I’ve done water changes for 3-5 days in a row n bigs at that. 50%’ers n I kno it’s not the safest for my little guys but at this point I had no choice. This tank has been in action for about 1-1/2 years or so. Lost some fish along the way n it’s very upsetting.
Thank you Vince

Hi Vince,

If you are getting detectable levels of ammonia, it’s possible you need to cycle (or if you have in the past, re-cycle) your tank. If ammonia won’t go down, it’s typically because the cycle isn’t established.

Read this guide for more info.

Hi Ian. I’m back again. So glad you are available. Once before I had green water.
You had advised me to add a polishing cloth which I did and my tank cleared up. It was great. Last week I did a water change and removed all water except 7 inches from the bottom of my 29 gal tank. The next day I had cloudy green water. I immediately applied the polishing cloth. Not the exact size but close to it but tank is still green. I did use Tetra water treatment conditioner when the tank was filled. I did loose 1 albino frog. The other one is fine and so are my 12 fish. Thanks Ian

Hi George,

When you say the polishing pad isn’t the right size, is the water is flowing around it? In order to trap the green gunk, water needs to flow through the pad. Any gaps here will mean these tiny green pieces can make their way back into your aquarium and multiply again.

Also, what are your ammonia, nitrite and nitrate levels reading?

I only ask as it’s unusual for green aquarium water to appear after such a large water change.

Can you use this aquatic fish conditioner for your own personal tap water consumption in order to detoxify water to cook and for tea and coffee and for safer drinking water for my cats ???
Thank you

Hi Karin,

Unfortunately water conditioner is not food grade. You would need to research an alternative method to make drinking water safe.

Chlorine in the amounts that is used in drinking water is NOT toxic to you if you drink it. The reason it hurts fish is because they breathe it in, and it harms their gills. Chlorine is used in tap water in these amounts because it prevents the growth of harmful bacteria without harming people. It’s been very well tested, it’s safe.

If you’re very worried, or if the water quality in your area is extremely poor and unsafe for other reasons, look into a home RO unit. It will remove just about everything from your water that isn’t water.


I’ve had my tank up and running for 5 weeks now with some fish in but my ammonia and nitrite levels are still dangerously high. My fish are eating and seem to be doing fine except they are breathing really fast. I do regular water changes and also use the likes of seachem prime, api QuickStart/stress zyme but nothing is working it just seems like my cycle hasn’t even started yet. I have a 350litre tank with 1 air pump and 2 external filters. Do you have any ways I can get this sorted ASAP so my fish don’t die?

Hi, Thanks for all the great info. I’m mourning the loss of yet another sweet betta. For some reason they all are dying at around the 7 month mark. I have a 2.5 gal heated and filtered tank, do weekly 20% water changes, etc. Whenever I test the water the parameters are great. I don’t know what on earth i’m doing to kill all these poor fish. I have one nerite snail. Now i’m trying to get my tank in order to try again. I actually have a RO system but have never used it for my fish. Given the choice, would you prefer RO water with the remineralizer or tap water with the Seachem Prime? Or, if I use RO water, would you use Seachem Prime only when needed for a spike in ammonia or nitrite? Thanks so much. BTW, I’m open to getting a larger tank if you think it would be helpful.

Hi Susan,

When you say your tank parameters are great, what are the readings for ammonia, nitrite, nitrate, pH and water temp?

Unless you have excessively hard water, using RO water complications the process and in many instances is unnecessary.

Hi Ian,
Well, today with just my lonely snail…
ammonia – 0
nitrite – 0
nitrate – 0-20 (it’s a test strip, hard to tell exactly)
pH – 6.5
water temp is 78

After the fish died (euthanized) 4-5 days ago I did at least a 75% water change. When I’ve had the fish in there, I’ve not seen these parameters really deviate which i know can’t possibly be accurate. Like I said before all these fish are living until about the 7 month mark and they start clamping fins and hiding and gradually go down hill from there.
Thanks so much for any advice!

Hi Susan,

I highly recommend buying an aquarium test kit, so you can be precise with your measurements. I recommend the API master test kit, it’s cheapest, will last years and should have everything you need to test your entire tank.

When testing, make sure you test outside in natural daylight. Indoor lighting can make the colors look off, leading to incorrect results.

If everything looks normal, speak to your local fish store (not petsmart or petco) they will be using the same water source as you and be able to offer more guidance.

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