The translation of this article can begin.

5.5.3. Water Conditioners

Photo of author

Author : David Bogert

Published :

Time To Read :
6 minutes
Difficulty : Level 7

Excerpt :

Most water supplies in the developed world have either chlorine or chloramine in them to kill bacteria and prevent disease outbreaks. This chlorine and chloramine need to be neutralized before it gets to the gills of a fish as it is very toxic to the fish. This is done with something called a “conditioner”. All ... Read more
5.5.3. Aquarium Water Conditioners
5.5.3. Aquarium Water Conditioners

Most water supplies in the developed world have either chlorine or chloramine in them to kill bacteria and prevent disease outbreaks. This chlorine and chloramine need to be neutralized before it gets to the gills of a fish as it is very toxic to the fish. This is done with something called a “conditioner”. All conditioners work with both chlorine and chloramine.

My recommendation with conditioners is simple:

Buy ONLY Conditioners that say “Sodium Thiosulfate” on the Bottle in the Ingredients List. Then use 5X the Recommended Dosage.

When I used to have chlorinated water for a 50 gallon (189,2 liter) tank 50% water change I would take the amount of thiosulfate conditioner which would, per the bottle, condition 25×5 or 125 gallons (94,6×5 or 473 liter)of water and add it to the 25 gallons (94,6 liter) that was left in the aquarium after draining. Thiosulfate is just very harmless, even at a 10x concentration. Then I would refill the tank with water above 70°F (21°C). Easy.

And this is not rocket science. Anything from a 2X to a 10X dosage is just fine. Just do not leave fish sit in chlorinated water for any length of time. Both chlorine and chloramine are very bad for fish, even for just a few minutes.

Image of aquarium fish Parrot Cichlids
Parrot Cichlids

Points to Remember About Conditioners

The subject of conditioners is quite complex and best left to the chemists. But there are a few salient points:

  • All conditioners neutralize roughly 1 to 2 ppm of chlorine or chloramine in a water supply.
  • All conditioners do ABSOLUTELY NOTHING to ammonia, nitrite or nitrate. This is ALL marketing hype. There are NO exceptions to this point. NONE!!! The articles below have a whole series of scientific tests which prove these products do not do what they say. Others have replicated these tests and come to the same conclusion.

If the conditioner bottle says on the bottle that its ingredient is sodium thiosulfate, then these two points are the only important points. If the bottle does not say sodium thiosulfate then some other points are important:

  • Never use more than five times the level recommended
  • Never use with a formalin based medication such as Ich-X

This is because most of these “mystery ingredient” conditioners have formalin to stabilize the conditioner. This can result in an overdose of formalin in the tank. Because of these limitations I do not recommend using anything but conditioners which state on their bottle they are sodium thiosulfate.

Nimbochromis Venustus
Nimbochromis Venustus

How to Use Conditioners

Note that the thiosulfate chlorine remover should be added to the water in a bucket or some such container, stirred and allowed to work for a few minutes before it is added to the aquarium. When a reaction is working on a level of one to two parts per million it takes a few minutes for every atom of the chlorine to be found by the neutralizer. It takes a few minutes longer if there is chloramine as the chloramine has to dissociate into chlorine.

But note that the effect is slight. Conditioner also removes the pink color of potassium permanganate. If one adds conditioner to this pink water the speed with which the pink color is removed is pretty fast.

Many hobbyists avoid adding the water to the fish aquarium and then adding the neutralizer. Chlorine is just a very bad actor for fish. But many very experienced hobbyists add water this way. If using buckets it is easy just add the chlorine neutralizer to each water change in the buckets for the water change, before putting the water in the aquarium. If one fills with a hose or a Python one has to add the neutralizer to the half drained aquarium before adding the water-change water.

More about that under this link:

5.5. Chlorine and Chloramine

The only problem with sodium thiosulfate products is that some of these products claim to neutralize the ammonia in chloramine, they don’t do that!

aquarium fish photo Amphilophus X Vieja Purple Rose Queen
Amphilophus X Vieja – Purple Rose Queen

Products Other than Conditioners

Note that many other products claim to be beneficial when added to new water or water for water changes. These products are all marketing scams which need to be avoided unless you have money to burn. These “snake oils” are generally of two categories:

The first category is the “Bacteria-in-a-bottle” products, like Seachem Stability and the various “zyme” products. These products do not work. Here is a test debunking these items:

2.8. Bacteria-in-a-bottle

Secondly there are the “Stress Coat” type products. Some of these products have some form of conditioner in them which will neutralize chlorine. But one of these products, API StressCoat Natural, Pond and Marine, claims to neutralize chlorine with aloe vera alone. It cannot neutralize chlorine and several Facebook group posts have had whole tanks killed by using this product as a chlorine conditioner.

Aloe vera is used in “stress coat” products (API StressCoat, Microbe-Lift Aquatic Stress Relief) supposedly to aid in fish diseases and after a water change to sooth the fish. Aloe vera coats the gills of the fish and interferes with oxygen exchange. It also rapidly depolymerizes, forming sugar in the aquarium water column. This sugar will give a bacterial outbreaks in the water column. This bacterial outbreak will kill fish. I do not recommend using these products.

More about stress coat products can be found at this link:

5.5.4. Stress Coat Products

picture of an aquarium fish Protomelas Spilonotus
Protomelas Spilonotus

Ascorbic Acid

Some use is made of ascorbic acid as a cheap remover of chlorine in chlorinated waste steams dumped into rivers and the like. Ascorbic Acid is a mild reducing agent so it will remove chlorine from the water. But it is an organic compound which is a food source for bacteria in the water column. And bacteria in the water column are always bad for a fish’s health. We do not recommend its use.

Homemade Conditioner

Simple homemade conditioner can be made by dissolving 32 grams of sodium thiosulfate in one cup of water. You don’t want to mix up too much as the solution does go bad with time (like two years time). Add one teaspoon of the solution per 50 gallons (189 liter) of the water to be treated. Since there are 100 drops in a teaspoon, this is a rate of two drops per gallon (3,79 liter).

Further Reading

There are some aquarium hobbyists who are interested in delving deep into the science and the calculations behind all aspects of the hobby. For those who are so inclined the following is pertinent: “Ammonia Detoxifying” Claims Seachem Prime and Safe Water Conditioner Chemistry Water Conditioner Cost Water Conditioner Testing Review Of Water Conditioners