Filtration
Canister filter
The right answer for large or heavily stocked tanks. Media volume is many times that of a hang-on-back unit, everything sits outside the tank, and flow can be directed precisely. The costs are price, a more involved service routine, and the fact that a leak is a flood rather than a puddle.
Short answer
A sealed external canister containing several litres of media, plumbed to the tank with inlet and outlet pipes. The highest capacity option and the quietest.
What it does
- High-volume mechanical, biological and chemical filtration
- Directed return flow, often via a spray bar
Strengths and where it fits
Strengths
- Very large media capacity
- Quiet in operation
- Equipment hidden outside the tank
- Flow direction fully controllable with spray bars and lily pipes
Good fit for
- Tanks above about 150 L
- Heavily stocked tanks
- Planted tanks needing directed flow
- Rimless display tanks
Limitations and where it is the wrong choice
Limitations
- Expensive
- Servicing is a longer job and involves disconnecting hoses
- Airlocks after maintenance are common
- Seal failure or a loose hose can empty a substantial volume onto the floor
- Less surface agitation than a hang-on-back unit unless the return is aimed at the surface
Poor fit for
- Small tanks, where the flow is excessive
- Keepers who want a two-minute service routine
Sizing
- Aim for a rated flow of roughly four to six times the tank volume per hour for a general community tank; more for messy fish or high-flow species.
- Rated flow assumes empty media and no head height. Real throughput is substantially lower.