MT, if you have string algae near the top on the sides of your pond, or on your waterfall, lower the pond or shut off the waterfall and do like Sissy does. She takes peroxide and I think she dilutes it with water, then sprays it on the algae after you lower the water. Let it dry in the sun, and it will die. Then use a brush and scrub it off as best you can, raise your water or turn on the waterfall, and it will be gone. I did a drastic thing last year, string algae was really bad, growing 6-8" a day on the sides west side of my pond. I poured full strength peroxide over the algae on the edge. I didn't just dump it, but splashed it a little at a time along the edge. It DID get rid of the algae, but I would never do it again, as it also made my water brown and murky for about a month. At least that's what I blame for the brown water. The water changed colors about a week later, but I later thought back and figured it was the peroxide. I didn't lose any plants or lilies, they were all fine, but I'm sure slower to grow because of the peroxide. This year, if I get it, I'm going to lower the water and spray it on the algae, as it seems to grow on the top few inches of water anyhow.