Photo: Ofkun · CC BY-SA 4.0
filtration
Aquarium filter media
By Fishy Dave
Mechanical foam catches gunk. Ceramic holds the bacteria that finish the nitrogen cycle. Carbon is optional and saturates. Stack coarse to bio to fine, rinse bio media in old tank water only, and stop buying disposable cartridges when foam will do.
Three jobs, one stack
Filter media is not one product. Mechanical media (coarse foam, sponge, floss) catches uneaten food and waste so it does not smother everything downstream. Biological media (ceramic rings, sintered glass, mature sponge pores) holds the bacteria that turn ammonia into nitrite, then nitrate. Chemical media (activated carbon, polish pads, specialty resins) is optional. It adsorbs some dissolved junk, then saturates and stops helping.
This page is the media literacy layer on top of the filter boxes we already cover. A sponge filter is mostly one foam cylinder doing mechanical and biological work with air. A hang-on-back filter is a rim basket you stuff. A canister filter is stacked trays under the stand. Same three jobs in each case.
Coarse first, then bio, then optional carbon
Put coarse foam or sponge first in the flow path. Fine polish pads and carbon belong last, if you use them at all. If sludge hits ceramic first, pores clog and flow collapses. Canister trays and AquaClear-style baskets are laid out for that coarse-to-fine path. Follow it.
Carbon is not the biofilter. Tossing a disposable combo cartridge every week throws out bacteria you paid to grow. Once a HOB basket accepts loose media, reuse foam and ceramic and leave carbon for short jobs. Established tanks often run foam and ceramic alone.
Cleaning without resetting the cycle
Squeeze foam in a bucket of old tank water when flow slows. Never tap water. Chlorine kills the nitrifiers living in the pores. Rinse ceramic the same way. Stagger cleaning so you do not wipe every layer the same day. A seeded sponge on the same tank can carry bio through a HOB or canister service.
How you cycle the tank still matters more than brand names on bags. Seed new media from an established sponge or filter when you can. Our cycle guide covers fishless ammonia dosing and the patience problem. Weekly water changes keep nitrate in check after the biofilter is online.
What to buy
The picks below are reusable AquaClear-class foam, Fluval BioMax ceramic rings for the bio stage, and optional Fluval carbon bags for short chemical jobs. Buy foam sized to your filter. Cut sheet foam only when your basket has no branded insert. We may earn a commission if you buy. See the affiliate disclosure.
What we would buy
AquaClear 20 foam inserts, 3-pack
Reusable coarse foam is the stop-buying-cartridges pick for AquaClear-class HOBs. It catches debris before ceramic, grows bacteria in the pores, and lasts through many squeezes in tank water. Same foam we already trust on the hang-on-back page.
Match foam size to your filter model. 30 and 50 packs exist for larger AquaClears. Never rinse under the tap. A foam sheet cut to fit works in some other baskets if your brand skips sized inserts.
See this listingFluval BioMax ceramic rings, 500 g
Porous ceramic rings for the biological stage in HOB baskets and canister trays. They hold nitrifying bacteria through a mechanical clean if you stagger the work. Same BioMax we list as extra media on the canister page.
Rinse only in old tank water. Do not replace every ring at once on a cycled tank. Skip a second bag if ammonia already stays at zero with the foam and stock ceramic you have.
See this listingFluval Carbon, 100 g nylon bags, 3-pack
Optional chemical stage in pre-filled bags that drop into a canister tray or a HOB basket behind the foam. Useful after a medication course, for tea-stained water, or when you want short-term odor control. Not a substitute for water changes or bio media.
Replace roughly every month while you are using it, then leave it out if the tank stays clear. Remove before dosing meds that need to remain in the water. Skip this pick if foam and ceramic already keep the tank stable.
See this listing
Frequently asked questions
What is the right order for aquarium filter media?+
Coarse mechanical first so sludge does not bury the bio layer, then ceramic or other biological media, then a fine polish pad or carbon only if you want it. That order matches how hang-on-back baskets and canister stacks are meant to run.
Can I rinse ceramic bio rings under the tap?+
No. Chlorine kills the nitrifying bacteria living in the pores. Squeeze foam and rinse ceramic in a bucket of old tank water during a water change. Stagger the work so you never wipe the whole stack in one day.
Do I need carbon in every filter?+
No. Carbon removes some organics, odors, and meds, then saturates. It is not the biofilter. Many established freshwater tanks run foam and ceramic without monthly carbon swaps. Pull carbon before you dose medication that needs to stay in the water.
Should I keep buying disposable HOB cartridges?+
Usually not, once you have a basket that accepts loose media. Stuff reusable foam and ceramic instead of tossing a combo cartridge every week. You throw less bacteria away and spend less on plastic. See our hang-on-back filter page for basket sizing.