Crystal Plex is a liquid copper sulfate solution designed to kill and control algae and some aquatic plants including Hydrilla. Pond algae treatments should be done on actively growing algae and when water temperatures are at least 50 F. Controls many types of algae like filamentous, chara, and planktonic for a beautiful and safe pond all year long. When used as directed, 100% safe for humans, fish, livestock, pets, birds, swimming and irrigation.