I have a very similar scum on my pond. I already have aeration from the bottom. Scum appears reddish with white bubbles. Completely disappears after hard rain but reappears next day. Have tried copper sulfate and that appears to work temporarily. I'm working feverishly to cut off nutrient supply at it's source. Am going to try the 2,4-D Amine and see if it is longer lasting for me.
