Black Pond Dye provides a mirror like reflective surface to your pond or water feature and prevents the growth of unsightly green algae and blanket weed. Black Pond Dye is commonly used by landscape gardeners and uses a safe, economical dye that restricts the light from the sun penetrating the water column, therefore cutting off the light source which causes algae and blanket weed to grow. Black Pond Dye is safe for use with emergent and floating aquatic plants and helps to protect fish from predators such as herons. Harmless to all other forms of life in the pond.