Algae Destroyer Liquid is best used when the water temperature is low (between April 1 and June 15). Higher temperatures cause rapid decay of weeds and algae, reducing the oxygen content of the water.... More If water temperature exceeds 75 degrees (F), extra aeration is required to avoid fish stress. Pond Care Algae Destroyer controls the growth of many types of algae in fountains, koi, goldfish and garden ponds. Algae Destroyer should not be used in aquariums and ponds containing live plants (Use AlgaeFix in aquariums and ponds containing live plants). One fluid ounce of Pond Care Algae Destroyer liquid treats 60 U.S. gallons .