SANCO COPPER SULFATE Pond Algae ControlCrystal Blue Copper Sulfate is a great pond algae control product for filamentous or string algae. Copper sulfate should be used as a pond algae treatment on actively growing algae in water temperature above 60F. When getting rid of algae in a pond, it is always important to treat 1 2 of the pond algae at a time to avoid killing too much algae and depleting the water of oxygen. Copper sulfate is safe for most varieties of fish (see restrictions below)