Guide
Types of aquarium filters
HOB, canister, sponge, internal: how they work and what to pick.
Aquarium filters come in several designs. Each type moves water through media to provide mechanical, biological, and sometimes chemical filtration. See filtration 101 for the basics. Here’s how the main filter types work and their pros and cons.
Hang-on-back (HOB)
HOB filters hang on the rim of the tank. Water is drawn up through an intake tube, passes through media in a box on the back, and returns via a spillway. They create surface agitation and are easy to install and service.
Pros: Affordable, easy to maintain, good surface agitation, widely available. Cons: Visible on the tank, limited media space, can be noisy if not adjusted. Good for small to medium tanks and beginners.
Canister
Canister filters sit below the tank, usually in the stand. Water is pumped from the tank through intake and return hoses into a sealed canister filled with media, then back into the tank. They hold more media and often run quieter than HOBs.
Pros: High capacity, hidden from view, powerful flow for larger tanks, flexible media options. Cons: More expensive, heavier to service, requires priming. Ideal for medium to large tanks. See comparing filters for side-by-side choices.
Sponge
Sponge filters use an air pump (or powerhead) to draw water through a porous sponge. Bacteria colonise the sponge for biological filtration; the sponge also traps debris. They sit inside the tank, often in a corner.
Pros: Cheap, gentle flow, safe for fry and shrimp, excellent biological filtration, no impeller to clog. Cons: Less mechanical filtration, takes up tank space, needs an air pump. Great for breeding tanks, hospital tanks, and low-flow setups.
Internal
Internal filters sit fully inside the tank. A small pump pulls water through a cartridge or media chamber and returns it. They’re compact and self-contained.
Pros: No external plumbing, easy to set up, good for small tanks and nano setups. Cons: Visible in the tank, limited media capacity, can be weak for larger tanks. Often used as a backup or in small aquariums.
Choosing a filter
Match the filter to tank size, stocking level, and fish needs. Heavily stocked or messy fish need more capacity; gentle species may need baffled flow. Ensure your filter supports a stable cycle and adequate turnover. Compare options in comparing aquarium filters.
Quick takeaways
- HOB: hang on the back, easy and affordable; good for small to medium tanks.
- Canister: high capacity, hidden; best for larger tanks.
- Sponge: gentle, biological; ideal for fry, shrimp, and low-flow setups.
- Internal: compact, in-tank; suited to small and nano tanks.
More guides · Filtration 101 · Comparing filters · Cycling a tank · App-aquatic