when i first started i bought 2x54w T5 HO retro kit new and put them over a 55g tank. I had some crazy hair algae that i couldn't keep up with. then i upgraded to a 75g with 2x250w MH and never saw it again! now i just added the T5s to the MH and went away for 2 days for work. when i came home i have TONS of algae growing all over glass! the only other thing i changed was i put on an empty canister filter that is putting a lot of micro bubbles in the tank so that could also be causing it?