In early Spring this year we had algae growing in the lake and ponds. I used Barley straw in mesh bags in the stream and ponds to kill the algea and stop new growth, as the Barley straw breaks down it releases algae killing enzimes. It can take over 200 lbs of straw for a 1 acre lake but for small ponds it does not take much. I used 1 bale about 40 lbs for the lake and small bags 5 to 10 lbs each in the ponds. Barley straw is best applied in early spring, before algae normally begins to grow, even at the start of Winter to get a jump on it. Put the Barley straw into mesh bags and submerged 2-3 feet below the water surface. I also put it in the stream. The algae was gone a 3 weeks later and my neighbors lake down stream also cleared of algae. If you have a small pond, a bale of Barley Straw is not expensive and can keep in a dry area for years if you don't need all of it that season. The Barley will not harm your fish and has no weed seeds to cause more problems. My Koi like to use the mesh Barley bags as their spawning media.