Water Dechlorinator: How It Works and How Much to Use in Aquariums

Many fishkeepers are unclear about water conditioners for aquariums – how they work, potential risks from overdosing, and the differences amongst the many brands of dechlorinators. Let’s discuss water conditioners based on our extensive experience and research.

Are Fish Really Require Water Conditioners?

Maybe. Most likely, your water is treated with chemicals such as chlorine or chloramine to kill bacteria, viruses and other microorganisms. These chemicals are toxic to aquatic animals and beneficial bacteria and therefore must be removed from the water using a dechlorinator. If you forget to add water conditioner to the tap water, your fish’s gills may become burned, causing them to start gasping or breathing heavily.

Your aquariums might not require water conditioner if your water comes from a well, or any other source of water that has not been treated with chemicals. You should have your well water tested for heavy metals. Some dechlorinators may be able to help.

Will letting water stand remove chlorine? Chlorine is extremely unstable and will eventually evaporate from water. Chloramine has been used in many water treatment plants as an alternative to chlorine. This is because it is a stable disinfectant that is formed by combining chlorine and ammonia. It is difficult to remove chlorine from water by evaporation. Instead, it must be neutralized with a dechlorinator. You can leave the tap water for up to 5 days to let chlorine evaporate. To speed up the evaporation process, aerate the water with an air stone for 12-24 hours or boil the water for 15-20 minutes. Multi-test strips can be used to test the water for chlorine and measure it.

To inject air into water, activate the surface of the water, and accelerate gas exchange, air stones are connected to an air pump with airline tubing.

What does a Dechlorinator do?

Water conditioners are used to reduce chlorine and chloramine in water and make it safe for fish to drink. Almost all dechlorinators contain sodium thiosulfate, which reacts to chlorine and chloramine to form harmless byproducts. Sodium Thiosulfate is often dissolved into water to make liquid dechlorinators. It looks similar to rock salt or white powder. Water conditioners may contain pH buffers, aloe verde to heal fish slime coats, and other additives.

Does dechlorinator remove ammonia? Some of them do, as stated on their packaging. Dechlorinators can only react to chloramine’s chlorine component when used to treat the substance. The remaining ammonia ions left in the water are toxic to fish, so some dechlorinators – such as Fritz Complete Water Conditioner, Seachem Prime, and Kordon AmQuel – contain extra chemicals that temporarily lock up the ammonia into an inert state (i.e., ammonium) for up to 24 hours. The ammonium can be consumed, and then further degraded by beneficial bacteria within your aquarium or filter.

While all dechlorinators neutralize the chlorine and chloramine, some include extra chemicals to remove ammonia, nitrogen, and heavy metals.

Can dechlorinator remove bleach quickly? The amount and concentrations of bleach used determine how much dechlorinator is required. As a starting point, see the directions for neutralizing Purigen chemical filtration media after it has been soaking in a bleach solution.

Is Dechlorinator Harmful to Fish?

Generally speaking, no. There are rare cases that it can be dangerous. The reducing agents in dechlorinator use up oxygen when removing chlorine from the water, and this reaction could be hazardous in poorly oxygenated tanks. Goldfish and discus aquariums, for example, can need large water changes of up to 90%. If water is low in oxygen, adding a lot of dechlorinator can further deplete oxygen levels, which could lead to the death of beneficial bacteria and fish.

To prevent this, most fishkeepers increase surface agitation in the aquariums to increase gas exchange. This refers to the process by which carbon dioxide (CO2) is expelled and new oxygen is added to the tank. However, hobbyists with high tech planted aquariums that inject pressurized CO2 often seek to minimize surface agitation. This is done to reduce gas exchange and allow more CO2 to remain in the water for plants to use. This is combined with the fact that plants consume most CO2 in the daytime, and then consume oxygen at night. Therefore, if you do a water change in the early morning right as the lights turn on, the dissolved oxygen in the water will be at its lowest point. Adding low-oxygen water and dechlorinator could be a recipe for disaster for your aquatic animals.

What is the recommended amount of dechlorinator per gallon?

Each dechlorinator’s dosing instructions are different. Fritz Complete recommends that you use 1 ml dechlorinator for every 10 gallons. What makes these directions a little confusing is that different municipalities use different amounts of chlorine in their water, so how do you know what is the right concentration for your water? Because the manufacturers of dechlorinators don’t know what chlorine is used in your area, they have made general guidelines that should hopefully be sufficient to cover tap water.

Fritz Complete contains an easy to use pump head for dosing 1ml of dechlorinator in 10 gallons water.

How long does dechlorinator take to work? Many companies recommend that you add the dechlorinator directly to tap water in separate containers before adding it to your aquarium. That being said, we always add the water conditioner directly to the aquarium and then pour in fresh tap water, and there have never been any problems.

Do you think you have too many dechlorinators in your fish tanks? Fritz complete allows you to dole out up to five times the recommended dose within 24 hours. This is a large range, so there’s a lot of room to make mistakes. Just keep in mind that potent concentrations of dechlorinator will quickly reduce the amount of dissolved oxygen, so it may be best to add an air stone for the next 3-4 hours to increase oxygenation in the water.

It wouldn’t be a bad idea to look up the average chlorine usage for your municipality and run a few experiments at home. Let’s say you find out your town uses 2 ppm (parts per million) of chlorine. If you do a 30% water change on a 100-gallon aquarium and you dose 3 pumps of Fritz Complete into 30 gallons of tap water, does the chlorine test register as 0 ppm? Is it possible to do without water conditioner or to eliminate all chlorine completely? The bottom line is to test your water for the lowest amount of chlorine and ensure that your fish have enough oxygen.

Use a multi-test strip for quick measurement of chlorine in your water.

Many people ask us for recommendations on the best dechlorinator. In truth, Fritz Complete Water Conditioner is our favorite because it has a super simple pump head that can treat 10 gallons per squirt. No more carefully pouring out liquid into a bottle cap and hoping you measured the right amount. You can do it in just a few seconds.