Many fishkeepers are unclear about water conditioners for aquariums.
Maybe. If your drinking water comes from a municipal water supply or other public water system, then most likely it is disinfected with chemicals like chlorine or chloramine to eliminate bacteria, viruses, and other microorganisms that can cause diseases. 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.
If your drinking water comes from a well or other water source that is untreated with chemicals, your aquariums may not need water conditioner. We suggest getting your well water tested to see if it contains any heavy metals because some dechlorinators can help remove them.
Does letting water sit remove chlorine? Yes, chlorine is fairly unstable and will gradually 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. Chloramine cannot be easily removed from water via evaporation and must be neutralized using dechlorinator. If you are sure your tap water contains chlorine and not chloramine, you can let the water sit for 1-5 days to allow all the chlorine to 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.
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. The remaining ammonia ions left in the water are toxic to fish, so some dechlorinators — such as Seachem Stability and Seachem Prime — 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.