Fritz ProAquatics Sodium Thiosulfate Pentahydrate can be used for the neutralization of chlorine (including chloramines) and/or iodine in water. Chlorine is toxic to fish and invertebrates so whenever chlorine is used, for example disinfecting tanks or equipment with sodium hypochlorite (bleach) or using tap water during transport or stocking, it is crucial to remove chlorine prior to the introduction of fish or other aquatic life.