I'm a FW
guy so I'm not sure my advice 100% applies, but I use Poly-fil (pillow stuffing) in my canister filter. You can buy a huge bag for $5 at Wal-mart or a craft store and it'll last for a year. I run it in the bottom tray of my Fluval 405 and I change it weekly so it doesn't have a chance to harbor too much beneficial bacteria and cause mini-cycles when I remove it. You'll be shocked how much fine debris it collects in that week. Just make sure you don't purchase a brand which is fire retardant, because that type is treated with chemicals. The one I get from Wal-mart is Fairfield brand (I believe).