Filter media: sponge, ceramic, carbon… which ones actually matter?
Three families of filter media share the work: sponge traps debris, ceramic houses the bacteria, carbon absorbs dissolved pollutants. The first two are essential and last almost forever; carbon is an occasional consumable, not permanent equipment. Equipment budget: 15 to 40 € depending on the filter.
What does each type of media do?
- Sponge (mechanical filtration): 5 to 15 €. Traps particles and debris. Coarse pore first, fine after. Rinses out and lasts for years.
- Ceramic rings and balls (biological filtration): 8 to 20 € per litre. Their porous surface houses the bacteria that convert ammonia — the engine of the nitrogen cycle.
- Activated carbon (chemical filtration): 5 to 12 € a pouch. Absorbs medication residues, tannins and yellowing. Saturated within 3 to 4 weeks.
- Filter floss: 3 to 6 €. Final water polishing — discard once clogged.
In what order should the media go in the filter?
Always follow the direction of water flow: coarse sponge first (it protects everything else), then fine sponge, then biological ceramics, and finally floss or carbon. In a small internal filter, a simple sponge-plus-ceramic pair is enough; external canister filters with baskets, compared in our guide to internal vs external filters, allow the full stack.
When to rinse, when to replace?
The rule that saves tanks: never clean everything at once. Rinse the sponges every 3 to 6 weeks in a bucket of tank water (never under the tap — chlorine kills the bacteria). Ceramics barely get rinsed, once or twice a year, and get replaced half at a time every 2 to 3 years when they start crumbling. Floss is thrown out whenever it clogs. Replacing all the media in one go, as some proprietary cartridges encourage, restarts the cycle and can trigger a lethal nitrite spike.
Is activated carbon actually useful?
Occasionally, yes: after a course of medication (it removes the residues), to clear water yellowed by driftwood, or against a suspicious smell. Permanently, no: once saturated it does nothing and takes up space better used by ceramics. Always remove it during treatment, or it absorbs the medication. More equipment guides in the accessories category.
Frequently asked questions
Are the all-in-one cartridges in kits a trap?
Often: disposable every month, they throw your bacteria away with the sponge. Replace them with loose sponge and ceramic — reusable and cheaper.
Can pozzolan be used instead of ceramics?
Yes, this volcanic rock from the garden centre (5 € for 10 litres) makes perfectly decent biological media. Rinse it thoroughly before use.
My water stays cloudy despite the filter — which media should I add?
Fine floss in the last position clears it in 24 to 48 hours. If the cloudiness is white and milky in a new tank, it’s a bacterial bloom: patience, no miracle media required.
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.