This past weekend I went down to Bill Cody's for a windmill. I'm still in process of assembly (it is a nasty thing to assemble). Anyways, my pond is 1/2 acre. 10 ft deep (to the top of the sludge layer). There is decades of sludge built up on the bottom. The surface is about 25-30% covered with duckweed (Bill already explained why this is a bad sign). I know the aerater will help a little and can't afford to have the pond rebuilt or dug out. I have been thinking of using Sonar/Avast to get rid of the duckweed. This should also control the duckweed for a couple years (according to directions). Is this a wise move? By keeping the duckweed from growing, would this help by NOT adding to the the sludge? Any other thoughts and suggestions would be much appreciated.