Yeah i used to have a prizm on my 30 gallon...it wasn't very efficent. I could leave it in there for a week and I would get half an inch of light green fluid! Now it could be that my tanks bioload is very small, but it just never seemed to work for me. The venturi on it that sucks in air always pissed me off cause it was always gulping air, but maybe thats how they all are, I am not really sure. I plan to get a Berlin Turbo Classic HOT Skimmer for my large aquarium when I get one.