the worm i fed was on the surface, but underneath a log that I turned over. The area I live in is pretty clean - no industrial pollutants or anything like that and we don't use chemicals in our lawn. I never treat the water before I change it because I ahve well water, which is in essence water taken from a river. I've never had any problems in that regard before. The wc was after the feed and I did not put a powerhead in there, instead i put some bubblers in. And yes the fish seemed fine before the wc