Treatment for irrigation water

I am an agriculturist and growing mainly cotton in my family farm. I use drip irrigation system for the irrigating the crop. We have a small farm pond, covered with polythene sheet to reduce the percolation of water. My problem is the constant growth of algae in water which creates problem in irrigation system. I am interested in exploring some new and cheap treatment methods for reducing this algae from the irrigation water so that drip doesn't have any problem. ( We have used barley straw to control the algae but it still there is formation of Algae in the pond. )