Fluidized bed filter is not a standalone type of aquarium tank filter because it provides only biological filtration and thus is often used in combination with either canister filter or external power filter to complement mechanical filtration part to remove solid waste particles. It uses a type of special sand or quartz as the filter media, and all these are initially loosely packed in the filter chamber. But as water flows through the compartment, it starts to expand and the constantly moving sand or quartz will form a fluidized bed that has wide surface area for growth of beneficial bacteria.

Fluidized bed filter is best used for new aquarium tank, which has just been set up. During this critical period, when ammonia will suddenly fluctuate, fluidized bed filter can help to act quickly to control and lower the ammonia level before it reaches the hazardous level that will harm your fish. The constantly moving stream of water through the bed will ensure oxygen rich water which will help the beneficial bacteria to establish faster and this will probably save you a lot of hassles later to maintain perfect water quality. Common fluidized bed filter sold in the market are also reasonably prized, with some units costing less than $100 suitable to be used to treat even for 50-gallon fish tank. In fact, the price here is still considered much lower than any other aquarium filtration system, for example like the diatom filter, which can amass huge cost of aquarium maintenance in the long run.