I have a 54 corner thats been set up for about a year and a half, and in the past 3 months or so the water has gotten really green. Now before i get replys about it bein an algea blum. I dont belive thats the case... and if it is its tubborn, ive been thru those with other tanks. now for tanks set up 54 corner, Aquaclear 70, H.O.T. magnum canister(rated for a 75gal) aquaclear 70 prefiltered power head. The tank is not near a window. lights normally on for 7-9 hrs a day, the last 3 weeks only when in workin on the tank do i turn the light on. I do my PWCs every other week of about 15-20 percent. after this started i jumped to 15 percent every week, and in the last 3 days ive done 2 40ish percent WCs. Does anybody have an idea of what this is or what to do to fix it(besides an undergravel becasue it has a sand subsrate, udergravel is the only suggestion ive gotten that i havent tried) Any help would be appriciated.