GreenClean Tablets - 3 lbs -  Algae Preventative.  Koi Pond, Fountain, Water Gardens, Water Features. EPA Registered. Safe for Fish, Plants, Pets and Wildlife. Safe for Fish, Birds, Pets and Aquatic Plants. When Used As Directed. Perfect for use water gardens, ornamental ponds, fountains, irrigation ponds and other water features Each 3lb container treats up to 6,800 gallons Chlorine, copper and phosphate-free EPA approved