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.