A dechlorinator is a chemical additive that removes chlorine or chloramine from water. Where tap water is chlorinated, it should be dechlorinated before use in an aquarium, since chlorine can harm aquatic life in the same way it kills micro-organisms. Chlorine will kill fish, and cause damage to an aquarium's biological filter. Chemicals that serve this function are reducing agents which reduce chlorine species to chloride, which is less harmful to fish.
Some compounds employed in commercial dechlorinators are: sodium thiosulfate, Sodium hydroxymethanesulfonate (used in AmQuel), and Sodium hydroxymethane sulfinic acid (used in Marineland Bio-safe).
See also
Aquarium Water Conditions
References
