I only use powered carbon filters so that I can regulate the rate and quantity of water flowing through the carbon filter. There is a sponge filter on the inlet side of the carbon and filter floss on the outlet side of the filter. I also put a layer of phosguard after the carbon so that I have a combo carbon and phosphate filter. Any phosphate being released from the carbon as well as any that is in the bulk water is caught by the phosguard.