It feeds off of nutrients. Prior to weekly water changes, with ro/di or distilled at the least, pull out as much as you can before you siphon water out of the tank. Reduce feeding, I only feed my tank twice a week with great results with fish that supposedly need daily feeding. It is a long process of getting rid of the stuff. If all of that does not help, you might want to look into ways to remove the phosphates/nitrates with things like GFO or an algae turf scrubber.