Been working on my own pond problem. First, what I thought was algae was identified as duckweed. The chemicals to control this is expensive, up to $300 per application for a small pond like mine. At a sports show, I was told that the grass eating carp (white amurs) would get the job done. I already used some to fix another weed problem and they worked. I was told that they eat less as they get larger and that mine were probably not eating enough to control the duckweed. I'll try more grass eaters, but it takes a couple of years to work. Still, better than expensive chemicals.