Barley Straw Pouches are the natural and effective way to control green water algae in garden ponds. Completely harmless to pets, wildlife and ponds, Barley Straw for ponds restricts the speed at which algae and blanket-weed grows in pond water, leading to a clearer pond. 1 Pouch treats 3673 litres (800 gallons). Also available in double pouches.