Your filter is only as good as what’s inside it. The stock sponges and cartridges most filters ship with are basic, and the cartridge-swapping model many brands push actually throws away your beneficial bacteria. Understanding filter media — and choosing the right mix — is the cheapest upgrade to water quality you can make. This UK guide covers the best filter media in 2026.
Here’s how to build a better filter.
- Stock cartridges are basic and swapping them throws away beneficial bacteria — build your own media mix.
- Use mechanical (sponge/floss), biological (ceramic/porous) and chemical (carbon) media.
- Layer flow: mechanical first, then biological, then chemical last.
- Never replace all biological media at once or clean it in tap water.
The three types of media
- Mechanical — sponges and floss that trap physical debris. Rinse, don’t replace.
- Biological — ceramic rings and porous media that house the beneficial bacteria that run your nitrogen cycle. Never clean these in tap water.
- Chemical — activated carbon and resins that remove dissolved impurities, used as needed.
Our top picks
Best biological media — Seachem Matrix / ceramic rings. Seachem Matrix or ceramic rings provide huge surface area for bacteria.
Best mechanical — filter sponge and floss. Filter sponge pads and filter floss polish the water clear.
Best chemical — activated carbon (as needed). Activated carbon removes tannins, odours and medication after treatment — remove it while medicating.
How to layer media and maintain it
Water should flow through mechanical first (to catch debris), then biological (to process waste), with chemical media last if used. Never replace all your biological media at once — you’d lose your bacteria and trigger new tank syndrome. Rinse mechanical media in old tank water, not tap water, so chlorine doesn’t kill the colony. See our filter guide.
Frequently asked questions
What is the best filter media order?
Water should pass through mechanical media first to trap debris, then biological media to process waste, then chemical media like carbon last if used. This protects the finer stages and keeps bacteria fed.
Should I replace my filter cartridge?
Avoid the throwaway-cartridge model — it discards your beneficial bacteria. Instead rinse mechanical media in old tank water and only replace it when it falls apart, keeping biological media in place.
Do I need carbon in my filter?
Not permanently. Activated carbon is best used as needed — to remove tannins, odours or leftover medication — and should be removed while dosing treatments, as it absorbs them.
— Jaqline Smalling, FishForever
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