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. Based on the available research and our years of experience using them, let’s talk about the truth behind water conditioners and answer your frequently asked questions.

Do Fish Really Need Water Conditioner?

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. You should add water conditioner to tap water to prevent your fish from getting burned. This could lead to them gasping heavily or gasping for air.

Water conditioner may not be necessary if the water is from a well or another water source that isn’t treated with chemicals. You should have your well water tested for heavy metals. Some dechlorinators may be able to help.

Can water sat down remove chlorine? No, chlorine is very unstable and will slowly evaporate from the water. However, many water treatment plants have begun using chloramine instead of chlorine because it is a more stable disinfectant formed by combining ammonia and chlorine. Chloramine cannot be easily removed from water via evaporation and must be neutralized using 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. Use multi-test strips to measure the water and make sure no chlorine is left.

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 Dechlorinator Do?

The main purpose of water conditioners is to break down chlorine and chloramine and make water safe for fish to inhabit. 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. Some water conditioners contain pH buffers, aloe vera to help heal the fish’s slime coats, or extra additives.

Does dechlorinator remove ammonia? Some of them do, as stated on their packaging. The main reason for this is because when dechlorinators are used to treat chloramine, they only react to the chlorine part of chloramine and not the ammonia part. Fish are unable to ingest the remaining ammonia ions in the water. Some dechlorinators, such as Fritz Complete Water Conditioner and Seachem Prime, contain additional chemicals that temporarily lock the ammonia into an inert (i.e. ammonium) state for up to 24 hours. The ammonium can then be consumed or further reduced by beneficial bacteria in your aquarium.

All dechlorinators neutralize chloramine and chlorine, but some have additional chemicals to deal with ammonia and nitrite.

Will the dechlorinator neutralize bleach? The dechlorinator reacts to bleach to remove it faster. 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.

Are Fish harmed by Dechlorinator?

In general, it is not. It is not dangerous in most cases. The reducing agents in dechlorinator use up oxygen when removing chlorine from the water, and this reaction could be hazardous in poorly oxygenated tanks. For instance, goldfish and discus aquariums can require huge 90% water changes. If you are using water with low oxygen content, adding lots of dechlorinator will further deplete the available oxygen, which can potentially suffocate your fish and beneficial bacteria.

Fishkeepers attempt to stop this happening by increasing the surface agitation of their aquariums to increase gas exchange. This is the process where carbon dioxide (CO2) escapes and new oxygen enters the tank. Hobbyists using high-tech, planted aquariums that infuse pressurized carbon dioxide (CO2) often want to reduce 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. If you water change your water in the early morning, right before the lights go on, the dissolved oxygen will be at its lowest level. Your aquatic animals could become sick if you add low-oxygen water or a dechlorinator.

How much dechlorinator should I use per gallon

Each dechlorinator has its own dosing requirements, so make sure to follow them. Fritz Complete recommends that you use 1 ml dechlorinator for every 10 gallons. This is because different cities use different amounts. How can you tell what the best concentration is for your water? The dechlorinator manufacturers don’t know the chlorine usage of each town so they make guidelines to hopefully cover all tap water.

Fritz Complete includes an easy-to use pump head that can be used to dose 1 ml dechlorinator for every 10 gallons.

How long does it take for dechlorinator to work? Since it takes about 2-5 minutes for chlorine and chloramine to be neutralized, many companies officially state that you should dose the dechlorinator to the tap water in a separate container before adding the water to the aquarium. We have never had any issues with the dechlorinator. Instead, we add it directly to the aquarium, then we pour in tap water.

Is it possible to put too much chlorine in your fish tank? Fritz Complete allows you to treat very high levels of nitrite and chloramine within 24 hours. This range is very wide and allows for a lot of room for error. 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 would be smart to research the average chlorine use in your area and do some experiments at home. Let’s assume your town uses 2 parts per million (ppm) of chlorine. What happens if you do an average 30% water change for a 100-gallon aquarium, and then add 3 pumps Fritz Complete to 30 galallons of tap water? Does the chlorine test register at 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 for our recommendation on the best dechlorinator to use, and honestly, we prefer Fritz Complete Water Conditioner because of the super easy pump head that treats 10 gallons of water per squirt. No more carefully pouring out liquid into a bottle cap and hoping you measured the right amount. Just a few quick pumps and you’re done.