I have heard the tumble method to, but when I look at other people's tanks their's are just stuffed in there and it looks all green and healthy. Maybe my light is the deal? I have only had the fuge up and running for maybe 2-3 months. I bought a shop light the kind with the aluminum cone, and put a 27 watt pc bulb in there that has a K rating of 6500 white. I know it has to be something simple. My sumps design is the same as the 20L built on melev's site.