Many Public and private water systems add chlorine to drinking water to destroy harmful bacteria and other organisms. Unfortunately fish are extremely sensitive to chlorine and even residual amounts can be toxic. Marchlor quickly removes toxic chlorine from tap water. Marchlor should be used when setting up, changing or adding water to an aquarium. It does NOT upset biological filtration balanceContent: 2 fl. oz in these wholesale discount cheap bulk chlorine remover. (59ml)Used in freshwater aquariums only.