Tetra Pond White Scale Control for your indoor and outdoor water fountains will prevent build up on your fountains. White Scale deposits form on the edges of water fountains when evaporation of hard water occurs. Hard water is water that contains calcium, and some city water supplies contain more calcium than others. White Scale looks like crusty layers of hard white deposits that form in a ring around the water line of your fountain. Monthly partial water changes and treatments of No More White Scale greatly reduces the chance for white scale buildup.