Each cube of frozen food you feed per day needs 12 square inches of screen, with a light on both sides totaling 12 real watts. Thus a nano that is fed one cube a day would need a screen 3 X 4 inches with a 6 real watt bulb on each side. A larger tank that is fed 10 cubes a day would need a screen 10 X 12 inches with 60 real watts of light on each side. If you feed flake, feeder fish, or anything else, you will need to blend it up super thick, strain out the excess water, pour it into a cube, and see how many cubes it is. And for Nori, 8 square inches = 1 cube.