Fairfax Water uses chlorine for disinfection purposes, which can be harmful to fish if not dechlorinated prior to placing fish in it. Fairfax Water utilizes two types of chlorine, free chlorine and chloramines (chlorine and ammonia mixture). Chloramines are normally used July - March, and free chlorine is generally used April - June. Free chlorine and chloramine dechlorination is performed differently. Chemical additives with directions for dechlorinating either free chlorine or chloramine from water for use in fish tanks or ponds are available at pet/fish supply stores.