The short answer
Neither is universally “better” — they suit different tanks. A canister filter wins on media capacity and quiet running, making it the choice for larger, planted or heavily-stocked tanks. A hang-on-back (HOB) filter wins on simplicity and price, and is perfect for smaller tanks and beginners. Pick by tank size, stocking and how much hardware you want hidden.
Canister filters: capacity and quiet
A canister sits in the cabinet below the tank, pumping water through large baskets of media and back up. Strengths:
- Big media volume — more biological, mechanical and chemical filtration, so it copes with big or heavily-stocked tanks.
- Quiet and hidden — the unit and hoses tuck out of sight; only the intake and outflow show.
- Flexible flow and CO2-friendly — spray bars and inline diffusers or reactors integrate neatly.
The trade-offs: higher cost, and servicing means disconnecting hoses and opening the canister — less often, but a bigger job.
HOB filters: simple and affordable
An HOB hangs on the tank rim, drawing water up and cascading it back through a media cartridge. Strengths:
- Cheap and easy — low cost, quick to set up.
- Simple maintenance — lift the lid, swap or rinse the media, done.
- Great for small tanks — plenty of filtration for nanos and community tanks.
The trade-offs: less media capacity, a slightly more visible presence on the back glass, and the cascade can add surface agitation that off-gases CO2 — worth noting for high-tech planted tanks.
Which should you buy?
- Small / lightly-stocked / budget — an HOB is ideal.
- Large / heavily-stocked / planted with CO2 — a canister earns its keep.
To choose properly, read how to choose an aquarium filter and do I need a filter at all. For canister recommendations see our best external filter picks and browse the full filters hub.