I have been running a magnum 350 for about a month now, which replaced my aquaclear 300. In the first hour of opperation, my tank was crystal clear... something that it had never been while using the AC. i've yet to open the thing up, because its running just fine... although today is cleaning day since the blue pad is full of chunks from the vacation feeder. I'd recommend my magnum 350. By the way, my tank is a heavily stocked 30 gallon tank. If you have the cash, go for the eheim pro model. From what i've read and seen, its by far the best of the canisters.