Water Conditioners for Aquariums 101

You may be tempted to use tap water in your aquarium. Tap water has chloramine or chlorine, which are added to make it safe for drinking. Chlorine and chloramine are toxic to fish. Water conditioners become necessary for aquariums as they eliminate these chemicals.

Water conditioners serve the primary purpose of breaking down chloramine and chlorine, thus making the water suitable for fish to survive. Sodium thiosulfate, found in almost all dechlorinators, combines with chloramine and chlorine to produce harmless by-products.

Sodium thiosulfate has the appearance of white powder or rock salt and is often diluted in water to produce liquid dechlorinators. Some water conditioners include Aloe Vera, PH buffers, or other substances to aid in the healing of the fish’s slime coats.

Adding a Water Conditioner to an Aquarium

When does an aquarium need a water conditioner?

A water conditioner comes in handy when the aquarium uses tap water. Tap water often has chlorine, which helps to eliminate germs and other pathogens that are harmful to humans.

Unfortunately, chlorine harms fish and makes an aquarium unfit for them. If there is too much chlorine, you may see your fish turn white before dying. If you’re observant, you’ll see that there are stressors in the aquarium.

Therefore, it is necessary to eliminate chlorine from aquarium water to make it favorable for fish to thrive. A water conditioner serves this purpose and will help to separate chlorine from tap water.

Notably, chloramine is a compound of chlorine and ammonia. While ammonia is an important part of the nitrogen cycle, it can be dangerous to aquatic life. It is critical to note that water containing chloramine is rather complex and may involve other processes.

For instance, the water conditioner will break the bonds between chlorine and ammonia molecules, leaving behind ammonia, which is also harmful to fish. Some water conditioners are specialized in eliminating ammonia too.

How a water conditioner for an aquarium works

A water conditioner is a compound that contains chemicals that are added to tap water before it is used in an aquarium. If there is only chlorine in the tap water, a simple conditioner with a dechlorinator can be employed.

In most cases, such a water conditioner may contain sodium thiosulfate, which converts chlorine to sodium chloride salt, which is less toxic to fish. Unfortunately, chloramine is currently the most commonly used purifier in tap water treatment. Simple dechlorinators can only remove the chlorine, leaving free ammonia that is extremely toxic to fish.

More complicated formulations use sulfonates, which can interact with both ammonia and chlorine, making them perfect for eliminating chloramine. 

The most advanced formulations include chelators that bind with various compounds and eliminate heavy metals and slime coat protectors. Such conditioners may include extracts from plants like Aloe Vera.

Can I add a water conditioner to a tank that has fish?

Adding a water conditioner to the tank with fish in it may not be dangerous if the amount of water changed in the tank is low. However, adding water conditioners to tap water is advisable before introducing the water into the tank with fish.

The reason is that chemical reactions may not go down well with the fish as some reactions are likely to be vigorous and dangerous to the fish.

Make a temporary home for the fish

If you had changed the water before conditioning it, you might consider removing the fish and keeping them in a temporary holding can as you condition the water in the tank.

However, if the water in question is in small quantities, you may consider adding the conditioner despite the fish’s presence, as the reaction is likely to be less vigorous.

It would be better to leave the fish in the tank while conditioning the water in a different container or tank. Leaving at least 25% of the water will likely reduce the fish’s chance of being stressed. It is also advisable to let the water stay for at least 24 hours after conditioning to give it enough time to complete all the chemical reactions.

Is too much water conditioner harmful?

Using too much water conditioner in a fish tank might hurt or even kill the fish. That’s because it will bind to the oxygen present in the tank and suffocate your fish.

The recommended amount of a dechlorinator comprising sodium thiosulfate is usually one teaspoon per 100 gallons of chlorinated tap water.

After dissolving the dried crystals in pure water, use the solution to eliminate chloramine or chlorine from the tap water you want to add to your fish tank. 

Apply 1 drop of the mixture per gallon of tap water, which also translates to one teaspoon per 100 gallons. Water with a high chlorine content may necessitate additional treatment. If you’re unsure about your water source, try two drops.

Water conditioner measurements

When measuring water codntioners, crystal doses are approximated by their dry weight rather than volume. On the other hand, the liquid volume is used to approximate the solution measure.

Excessive application of the dechlorinator in an aquarium with wish can cause skin and gills irritation, which could give way to infections that may also turn fatal. Therefore, avoid overdosing dechlorinators and maintain the doses recommended by the manufacturers.

Also, make a point of understanding how to measure water pH and know when dechlorination is required, as sometimes it may be unnecessary, while in some cases, a lot of it may be required.

How to add a water conditioner to an aquarium

When using tap water in aquariums, use sodium thiosulfate for fast chloramine or chlorine removal. Dosage rates vary depending on the water pH. However, rates of 1.5 to 2.5 parts of sodium thiosulfate to one part of dissolved chlorine should be sufficient.

Test a sample of the water to be changed to determine the minimal amount required for a specific change:

  1. Collect a sample of the water to be used and test for chlorine levels.
  2. Dissolve a quarter teaspoon of sodium thiosulfate into the sample (preferably 5 gallons) and give it some time to settle.
  3. Retest the total chlorine levels after adding the solution and waiting for about 30 minutes. If there are no chlorine traces, the preferred dosage rate would be a 1/4 teaspoon for every 5 gallons of water.
  4. If there are no positive results, use an equal amount of the solution in the same water. You can calculate the volume of sodium thiosulfate used per a given volume of water and know the best amounts to apply to the rest of the water.

How quickly does a conditioner work?

A good water conditioner may take about two to five minutes to completely neutralize chlorine in the water based on the volume.

Chlorine is a highly reactive substance that begins reacting with sodium thiosulfate instantly. It should take the shortest time possible for the substance to turn into salt (sodium chloride) as long as the quantities of the solution match the desired water quantities.

Exceptions and anomalies

Sometimes, people add conditioners to their tank waters, but no reactions are recorded. In such a case, there could be a possibility that the conditioner is expired or there is no chlorine in the water. Perhaps, while testing for chlorine, the results gave a false positive.

In other cases, the conditioner could have been left open for too long to the point that it reacted with the air and became obsolete. Some conditioners can combine with oxygen to produce other compounds.

This is why conditioners may become dangerous to fish if used in large quantities. The unused dechlorinator may react with the water’s oxygen, choking the fish.

Natural water conditioner for aquarium

There are various ways you can dechlorinate tap water without using chemicals. Some of them are very natural, while others are near natural. They include the following:

  1. Simply letting tap water sit for 24 hours will allow the chlorine to evaporate from it.
  2. Boil the tap water for about 8 to 15 minutes. Boiling the water will let the chlorine escape, leaving water that may be cooled and then used in a fish aquarium.
  3. Using vitamin C pellets which are also excellent in eliminating chlorine from water.
  4. Placing a UV light near the water container. UV breaks down chlorine.
  5. Reverse osmosis or carbon filtration can produce excellent results. Carbon filters trap chlorine and other chemicals in the water. Carbon reacts with chlorine to produce carbon tetrachloride (CCL4).

These first two methods depend on chlorine having a lower boiling point than water. Thus, it evaporates faster. The downside to the last three methods is that you have to purchase them.

Plants may purify the water in a fish tank, but they cant condition the tank since there is no record of plants that can remove chlorine or chloramine from water.

Natural vs artificial water conditioners

The main differences between homemade and artificial water conditioners include the following:

Natural/Homemade Water ConditionerArtificial Water Conditioner
Cheaper as most are free e.g., sunlight.Relatively costlier ($5-20)
Simple to use.Complicated and differ in instructions.
Little to no training needed.Requires expertise.
Take longer to work e.g., 24 for sunlight.Relatively fast (a few hours).
No dangers of overdose.It may be easily overdosed.
It guarantees zero harm to fish.If overused, they may be harmful to fish.
Natural homemade water conditioner vs artificial water conditioner comparisons


As a fish keeper, it is critical to understand the challenges that chlorine and chloramine cause to fish. On one hand, they make water safe for human consumption. However, they harm fish and other aquatic forms fo life.

The good news is that, it’s possible to separate the chlorine from the water to use in an aquarium. Water conditioners serve this purpose, making them essential components of aquariums.

Leave a Comment