Oase Aqua Activ AlGo Universal - Total Algae Control - 5L is an advanced pond treatment that works effectively against Blanket Weed (String Algae) and other algae within a pond. By specifically targeting the algae's metabolism it gradually kills the weed and helps prevent re-growth. This is a single dose treatment product which takes 2 - 3 weeks to see its full effect and should be used at a 50% strength once every 4 weeks to prevent re-growth.