You can add Barley straw. Use chicken wire to make one or two round balls about 18 inches each, add barley straw to fill. Put them in the pond, change the barley straw once a month and no more algae.You can also buy liquid barley concentrate at most home centers. Best thing about is no chemicals, all natural. Works great, I live in Ohio and it works very very well. Took all my plants out this year, tired of not being able to see my fish. Took about 3 days to be all clear.