Barley straw has been used for algae treatment for decades. Its decomposition produces a by-product that breaks down under sunlight, killing algae. This extract is the by-product for the decomposition process and delivers the natural algae control of Barley straw without the draw backs: - Works a minimum of 1 month quicker than Barley straw - Not all Barley straw decomposition produces the by-product - No need for ugly bails of straw in your pond. - Completely natural Treats 4,546 Litres.