After 6 weeks I may be winning. Have employed all the usual methods, but didn't think of reducing the photoperiod until it was mentioned here. It was also suggested somewhere that testing the tapwater was a good idea. It used to always be 0, but now I get a reading of 1.0. This may be why things got worse after all those water changes! It also seems to help if I give my filter media a real good wringing each day. It turns my bucket water dark green each time.