Improve the health and beauty of your pond with Gordon?s PondMaster ready-to-use formulation. Control aquatic algae and weed formations in water bodies with the Gordon's PondMaster Copper Sulfate Crystals. Designed specifically for aquatic use, it can be used in ponds, lakes, irrigation systems and ditches. The crystals control the formation of green and blue-green algae, weeds, diatoms and flagellates.