Your filter is the most important piece of equipment in your aquarium, and choosing the wrong one is one of the most expensive beginner mistakes. This guide breaks down every filter type, what each is best for, and exactly how to choose the right one for your specific tank.
What a Filter Actually Does
A filter performs three types of filtration:
- Mechanical: physically traps particles using sponge or filter wool
- Biological: beneficial bacteria colonise porous media and convert toxic ammonia to nitrite to nitrate
- Chemical: activated carbon removes dissolved pollutants, odours, and medications
Biological filtration is by far the most important. Never choose a filter based on mechanical filtration alone.
Filter Sizing: The Most Important Rule
Always buy a filter rated for at least double your tank volume. Manufacturers rate their filters under ideal conditions. For a moderately stocked 80L tank, you need a filter rated for 160L+.
Internal Filters
Best for: small to medium tanks (up to 100L), budget setups, breeding and quarantine tanks.
Pros: inexpensive, easy to maintain, no leak risk, good for beginners.
Cons: takes up space inside the tank, limited media capacity, less powerful than external filters.
External Canister Filters
Best for: medium to large tanks (60L+), planted tanks, high-stocking setups.
Pros: powerful, large media capacity, hidden, very quiet, excellent for planted tanks.
Cons: more expensive, more complex setup, small leak risk, require priming after maintenance.
Look for multiple media baskets, a self-priming button, and a minimum 3-year warranty.
Hang-On-Back (HOB) Filters
Best for: community tanks up to 200L, beginners who want simplicity with decent power.
Pros: easy to maintain, good surface agitation for oxygen, unobtrusive on the back glass.
Cons: noisy if water level drops, can off-gas CO2 in planted tanks.
Choose HOB filters with removable media baskets rather than proprietary cartridges; this lets you use your own ceramic rings and sponge.
Sponge Filters
Best for: shrimp tanks, fry tanks, quarantine/hospital tanks, supplementary filtration.
Pros: extremely cheap, gentle flow (won't suck up shrimp or fry), easy to clean, excellent biological surface.
Cons: requires an air pump, limited mechanical filtration.
Choosing Based on Your Tank Type
- Nano tank (under 30L): small internal filter or single sponge filter
- Community tank (30–100L): quality internal filter (rated 200L+) or entry-level external canister
- Planted tank: external canister with lily pipes or spray bar
- Shrimp tank: sponge filter only; any other intake will kill shrimplets
- Heavily stocked tank: external canister rated 3–4x tank volume, or two filters
Filter Media: What to Put Inside
Layer your media from water inlet to outlet: coarse sponge (traps large particles), fine sponge or filter wool (catches fine particles), ceramic rings or bio rings (biological filtration, never replace this), and optionally activated carbon (replace every 4 weeks).
Browse our full range of internal filters, external canister filters, sponge filters, and filter media in our Filtration & Pumps range.
