I found a new product called SuperCartridge. It is a replacement cartridge for Marineland and Tetra filters that has more surface area for bacterial growth and a removable foam insert that is impregnated with carbon for chemical filtering. I have used them on my Penguin BIO-Wheel 170 and 330 filters for about 3 months now. The even better news is that the replacement foam inserts are much cheaper than buying Marineland's Rite-Size cartridges. You can read more about them here.
I bought them online at Drs. Foster & Smith. Here is a link to that website.
Gene Heitman - 12 tanks (11 freshwater and 1 saltwater), 206 gallons, 20+ species of fish/shrimp/snails, 52+ species of plants ... 10 years ago I just wanted 1 tank with some fish