Why Filtration Matters
A filter does three things: mechanical filtration (removes particles), biological filtration (houses beneficial bacteria that process ammonia and nitrite), and chemical filtration (removes dissolved toxins via activated carbon). Biological filtration is by far the most important — the other two are secondary to keeping ammonia and nitrite at zero.
Types of Aquarium Filters
Sponge Filter
Best for: Small tanks (under 60L), fry tanks, betta tanks, hospital/quarantine tanks
A sponge filter connects to an air pump and draws water through a porous foam sponge. Bacteria colonise the sponge, providing excellent biological filtration. Flow rate is gentle — perfect for Bettas and fry. They are cheap, simple, easy to clean and nearly impossible to fail. The main limitation is that they provide no chemical filtration and limited mechanical filtration.
Hang-On-Back (HOB) Filter
Best for: Small to medium tanks (20–200L)
HOB filters hang on the back of the tank, drawing water up through a tube and passing it through filter media before returning it to the tank. They are easy to maintain — media cartridges slide in and out — and provide good all-round filtration. Brands like Resun and Atman are reliable and affordable.
Canister Filter
Best for: Medium to large tanks (80L+)
Canister filters sit below or beside the tank. Water is drawn through intake pipes into a sealed canister containing multiple chambers of media, then pumped back. They have a large media capacity (more biological filtration), higher flow rates and very quiet operation. Maintenance every 3–6 months involves opening the canister and cleaning the media in tank water. Sobo and Atman make excellent canister filters at a competitive price point.
Undergravel Filter
Best for: Bare-bottom tanks, older-style setups
Undergravel filters draw water down through the substrate, using it as the biological filter media. They work but are now largely outdated — they are difficult to clean, require bare gravel (no plants or fine sand), and can accumulate detritus beneath the plates. Not recommended for new setups.
Internal Power Filter
Best for: Small tanks, additional filtration
Internal filters sit inside the tank, fully submerged. They are compact, inexpensive and suitable for tanks up to 80L. Atman and Sobo make reliable internal filters. The downside is that they take up space inside the tank and must be cleaned more frequently than canisters.
Sump Filter
Best for: Large tanks (300L+), marine tanks, Arowana setups
A sump is a separate tank (usually below the main display tank) into which the display tank overflows. The sump contains biological, mechanical and chemical media and a return pump. Sumps have the largest media capacity of any filter type and are the gold standard for heavily stocked or large fish setups.
Choosing Filter Media
Mechanical: Filter foam/sponge (coarse to fine), filter floss, filter wool
Biological: Ceramic rings, bio-balls, pot scourers, lava rock
Chemical: Activated carbon (removes odours, medications, tannins), Purigen (removes organics)
Always place mechanical media before biological media in the flow path — mechanical filters remove particles that would otherwise clog and smother your biological media.
