Watts per gallon is not a good measure for T-5's because watts simply measure how much power they consume. With T-5's the reflector is what makes them so effective. I'm running 4*39w T-5's with Tek reflectors and I'm keeping Hippo, Squamosa, Derasa, and Crocea with a couple Maxima's planned all about 24 inches below the bulbs. I plan to move the crocea up once I figure out where I want to place it.