Aquatic Barley Straw is most effective when applied early in the year prior to the appearance of green sludge (especially in early spring). When applied to cold water, it may take six to eight weeks for the straw to begin producing the active chemicals that inhibit green sludge growth. Ideally you should start treating your pond just before Spring to ward off any green sludge problems that may occur. Take advantage of our bulk buys of Aquatic Barley Straw to tackle your green sludge problems today.