Crystal Blue Copper Sulfate Algaecide - Aquatic Grade Granular Pond Algae Control - 5 lbs 99% Copper Sulfate Pentahydrate Controls most species of algae like filamentous, string algae and swimmers itch Most effective when cast out on top of thick floating algae mats Granular Copper Sulfate, 5 Lbs Do Not Use with KOI or Goldfish