My filter is a Top Fin power filter that fits 20 gal tank. I have a 20 gallon, but I think the filter is lazy or something :P I turn it up on high sometimes, but I worry that the current will irritate my Axies so I keep it low sometimes. If the corner filters don't work very well, I'm not goign to invest money into them. I wanted to check with this forum before I bought any, becasue I don't know anything about them. I'll stick with my filter for now. If the worms come back, I'll get something stronger.