I use all 3. I have a pretty hefty bioload though. It really depends on your tank. I have a lot of fish and I keep them well fed so I use all 3 plus PhosE. Biopellets are cool, but if you start with too much at once you might run into problems. I had a small cyano outbreak when I doubled my pellets, nothing major though. Biopellets and GFO are for nitrates and phosphates, carbon for impurities and clarity.