A canister filter is a type of aquarium filter that is designed to provide efficient water filtration for both freshwater and saltwater tanks. It consists of a sealed container, or canister, that holds various filter media, such as activated carbon, foam pads, and ceramic rings. Water is drawn from the aquarium, passed through the filter media, and then returned to the tank, helping to remove debris, toxins, and impurities. These filters are popular among aquarium enthusiasts because they offer high flow rates and can accommodate larger tanks. They are also versatile, allowing users to customize the filter media based on the specific needs of their aquarium, such as the presence of fish, plants, or coral.