Zilla Basking Platform Replacement Filter Cartridges for Aquarium, 3 Pack Replacement filter cartridges for Zilla Deluxe and Premium Aquatic Turtle Kits (Basking Platform Filter 20G and Aqueon 10) Contains activated carbon and dense floss that traps fine debris Replace cartridges once monthly, when they get clogged or when water enters the filter bypass Simply remove used cartridge from the bio-holster, rinse new cartridge and insert new cartridge facing towards the "front" Do not clean the bio-holster when replacing the filter cartridge as it contains living beneficial bacteria