A dechlorinator is a chemical additive that removes chlorine or chloramine from water. Where tap water is chlorinated, it should generally be dechlorinated before use in an aquarium, since chlorine can harm marine life in the same way it kills microorganisms. Chemicals that serve this function are antioxidants or reducing agents. See redox for more information on chemistry, and Aquarium#Water conditions for more on conditioning aquarium water. General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... Chloramine (monochloramine) is a toxic substance (NH2Cl) created by the chemical reaction of ammonia and sodium hypochlorite (chlorine bleach) under alkaline conditions. ... Chlorination is the process of adding the element chlorine to water to make it fit for human consumption (potable) or to water intended for swimming or bathing in order to keep it from spreading disease. ... A 335,000 U.S. gallon (1. ... An antioxidant is a chemical that prevents the oxidation of other chemicals. ... Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... A 335,000 U.S. gallon (1. ...