Canister filters are large external aquarium filters that are best suited for medium to large tanks.
They typically sit underneath the tank in its stand or cabinet and stand over a foot tall. While specific operation and filtration materials vary depending on the make and model of the filter, they all operate in a similar manner. Water is pulled in though a tube that’s been placed in the aquarium, the water is then pumped through a series of increasingly meticulous filtration mechanisms. Each level of filtration sifts out larger and larger particulates until the water is clean enough to go back into the tank. When the water is pumped back into the tank, where it can either be deposited directly from the outgoing tube, or the flow can be diffused using a spray bar. The spray bar prevents introducing a current into a delicate aquarium environment.
If you want a filter that’s a cheaper filter, go with a Fluval canister filter, but if you’re thinking of going high end, you might want to look into an Eheim canister filter. While the extra cost of the Eheim will tend to balance out with a longer life, a Fluval will get the job done and will last a long time as well.
Your external canister filter does not require frequent maintenance like an in-tank filter. The maintenance on one of these filters is usually done every 4 months, though it’s not uncommon to find models that can go as long as a year without maintenance.
Canister filters are a model of efficiency because they physically push the water through the filtration system, where other systems passively allow the water to flow through them. This is why canister filters are ideal for larger tanks; they get a lot more done. These filters are also versatile in that you have a choice of what type of filtration is best suited for your tank, unlike other types of filters where you are stuck with their specific filters.
All in all a canister filter is a great choice for medium and large tanks, and will even work for your small tank if you’d like. Their power and efficiency simply make them a great all around filter.