Pond Block Helps Control Algae Growth in Ornamental Fish Ponds,"Offers an easy, effective way to control and prevent the growth of algae. Leaves pond water crystal clear. Helps keep pond clear from algae when used regularly. Pond block is not recommended for lilies or hyacinths.","Replace when fully dissolved (usually after 30 days). For best results, place the block in an area of the pond that is calm. Not recommended for Water Lilies and Hyacinths.",50 blocks,1 block/250 U.S. gal. (950 L),"12,500 U.S. gal. (47300 L)"