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. Your fish may start to gasp or breathe heavily if they are not given water conditioner.

If your drinking water comes from a well or other water source that is untreated with chemicals, your aquariums may not need water conditioner. It is a good idea to test your well water for heavy metals. There are dechlorinators that can help you get rid of them.

Will letting water stand remove chlorine? Chlorine is extremely unstable and will eventually evaporate from 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. It is difficult to remove chlorine from water by evaporation. Instead, it must be neutralized with a dechlorinator. To ensure that your tap water does not contain chloramine but chlorine, you can allow the water to sit for between 1 and 5 days. This will allow the chlorine to evaporate. The evaporation process can be accelerated by boiling the water for 15-20 minutes, or using an air stone to aerate it for 12-24 hours. Multi-test strips are used to measure the water.

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?

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. Some water conditioners contain pH buffers, aloe vera to help heal the fish’s slime coats, or extra additives.

Can a dechlorinator remove ammonia from chloramine? Yes, according to their packaging. This is due to the fact that dechlorinators only react to the chloramine part of chloramine when they are used to treat it. 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. During this time, the ammonium can be consumed and further broken down by beneficial bacteria in your aquarium and filter.

All dechlorinators neutralize chlorine and chloramine, but some contain extra chemicals to treat ammonia, nitrite, and heavy metals.

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

Is the Dechlorinator harmful to fish?

No. It is not dangerous in most cases. Dechlorinators use oxygen to remove chlorine from water. This reaction can be dangerous in tanks with low oxygen levels. Goldfish and discus aquariums, for example, can need large water changes of up to 90%. If your water has low oxygen content, you can add lots of dechlorinator to further reduce the oxygen. This could potentially cause fish death and harmful bacteria.

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. Hobbyists who have high-tech planted aquariums that use pressurized CO2 will often try to reduce surface agitation. In order to increase CO2 retention in the water, the goal is to reduce gas exchange. Combine this with the fact that plants only consume CO2 during the daytime and then they 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. 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’s dosing instructions are different. Fritz Complete, for example, recommends 1 ml per 10 gallons water. 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? Since the dechlorinator manufacturers do not know how much chlorine your town uses, they deliberately make general guidelines that will hopefully cover everyone’s tap water.

Fritz Complete comes with an easy-to-use pump head for dosing 1 ml of dechlorinator per 10 gallons of water.

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. However, we have never experienced any problems with adding the water conditioner to the aquarium. We then add fresh tap water.

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 would be smart to research the average chlorine use in your area and do some experiments at home. Let’s suppose your town has 2 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? Do you have to use more water conditioner to get rid of all the chlorine? Bottom line: test your water to use the least amount of dechlorinator you can get away and make sure your fish don’t run out of 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. There’s no need to carefully measure the volume of liquid in a cap or pour it into a bottle. You can do it in just a few seconds.