Aquarium & Fish Tank Filter Cartridges

Getting the right cartridge makes a real difference to water clarity and fish health, so it's worth checking both the size and media type before you order. Most cartridges combine mechanical foam to trap debris with an activated carbon layer for polishing and odour removal, and some include ceramic or bio-media to support the beneficial bacteria that keep ammonia and nitrite in check. Always match the cartridge to your specific filter model, as a loose or oversized fit lets water bypass the media entirely. If you're unsure which filter, and in turn which cartridge, suits your tank size and stocking level, our best fish tank filters: a practical buying guide can help you work it out. As a rule, replace or rinse cartridges every 2-4 weeks, alternating old and new media where possible so you don't strip out all your bacteria at once.