The natural solution to green water & blanket weed. When barley straw is added to water it begins to decompose & kill the blanket weed & algae. The rate of decomposition depends on the water temeperature. Usually within a week the Barley Straw breaks down & releases cells into the water. By the action of sunlight these are turned into humic acid, which is then converted into low level hydrogen peroxide. The hydrogen peroxide interferes with the formation of the algae, but does not effect invertebrates or fish.