I have a tank filled with healthy growing plants, running on Co2 about 6bps. Somehow I still have algae on the glass of my tank. This algae is hard to remove, and will only come off after i wipe the tank with filter cloth. However after a while the algae reappears again on the glass. Its so hard to get rid of them. My ottos seems to be eating them but not fast enough. Help please. Thanks.