Those results are good!! Does the algae grow real thick, as in off the screen. Mine was getting about 1/4" thick, maybe a hair more?? The screen should be sized to the amount you feed. Take for instance the frozen brine shrimp you can buy. They are in what looks like Ice cube trays. Imagine if you filled those with food you feed daily, how many cubes would you feed a day. I am only feeding about 2-3 of those per day so I re-did my screen to support 3 cubes. Each cube takes 12" of screen. So one cube would need a screen 3"x4" lighted on both sided. I made mine for 3 cubes which is 36", so I built it 6x6. If you are using a one sided it needs to be a little bigger then 12" per cube, maybe almost double-ish and lit very well. Mine was 9+"x6" which was way over kill and not a real thick green growth. I had good water tests the other way, my readings where always about zero.