I bought a 30 gallon tank a while back and thought I could run it on a couple small filters, but inevitably they failed to keep up and I was left with a very green tank that was a bear to clean each week. I bought this filter based on previous reviews and couldn't be happier! Here not even two weeks later my water is completely clear and my algae has disappeared. In fact I had algae that I thought had stained the silicon seal green, yet the seals themselves are almost perfectly clear again! The only one in the house who wouldn't give this a high rating is my plecostomus who now has to do detailed searches for food. And let me mention again that this filter is rated for up to 20 gallons, but I am running it in a 30 gallon tank and it works great!!