Emperor and aquaclears seem to be the best hang-on back power filters. Emperors have the biowheel like a penguin but are built better, last longer, and some have an extra water pump just to make the biowheel turn. Aquaclears last the longest out of any of them and have the most surface area for filter material. In my aquaclear 300 (70) I have a sponge i have used for a year, bio max ceramic noodles, and a top layer of filter floss in an old carbon insert bag. The sponge catches almost all of the debris and the filter floss polishes it off. oth emperors and aquaclear can be purchased cheaply online.