Our lake corporation had a guy come out and he told us that we could do that and that would help out algae problem (colonial and blue algae). Our problem was we wanted weeds in out lake for the fish. He suggested that we put Alumnium Sulphate in our lake at a rate of 125 pounds per acre to help the algae problem. We did so in April and so far we haven't had a problem with algae. The lake seems to be clearing up a lot and we will probably do it again next year. Just another thought of something that you may try.