The dry CleanMAX formula works very good on string algae. It kills string algae, also known as filamentuos algae, on contact. For best results turn the water flow off and allow the powder to settle on to the algae. You will notice it working and can clean up any loose debris before turning the water flow back on. Use all PondMAX water treatments as instructed on the packaging for best and safest results. This CleanMAX dry formula comes in the sizes 1lb, 2lb, 10lb and 25lb. There are options to cover sq. ft. of 400 sq. ft., 800 sq. ft., 4000 sq. ft. and 10000 sq. ft.