Canister filters are for use on Freshwater Aquariums and some light fish only Saltwater Aquariums. These filters are made to sit below the aquarium in the aquarium stand. There are intake and return Lines that run up the outside back wall of the aquarium fish tank and go up over the top into the aquarium through the filter slot. The filter slot is standard on all TRUVU Freshwater Aquariums. Canister filters are easy to service and a very affordable aquarium filtration choice.