thats a tetra whisper right? i have had one of those that came with a kit i bought, ditch the filter cartridges and get some fluval poly foam and cut it to size, it works much better imo. you will just need to keep the seeded filter media in for 4-6 weeks. for the peroxide, first you can just cut the filter media below the water line. then take the filter out and dip a paper towel in peroxide and wipe out the top of the filter. then run the filter in a small bucket of tank water and your good to go.