i've used one in the past and still use it on my 20g reef occasionally. for more than a 20g, it is utter and complete crap. useless. there are better options for 20g tanks even (like the bakpak skimmers). the thing is that skilters just suck as protein skimmers and can't handle it. as a power filter alone, it's actually pretty good IME...it never jams up and never stops during power surges or anything...