In one of my 20 Gallon aquariums, im having a real hard time getting rid of green suspended algae. I've covered it twice with towels for about 5 days each to try and kill it but it came back. Now im trying some Kent product that is supposed to clump the algae so it can be picked up by the filter. An Aqua Clear 30 (formerly called 150) but the problem persists. Has anyone got any tips at how i can solve the problem?