Saltwater Fitration Systems: Undergravel Filters

As noted in the past few articles, this is a continuation in a series of articles about aquarium fitration systems. This article will be an overview of undergravel filters.

Undergravel filters are among the two most popular filtration systems for saltwater aquariums (wet/dry trickle filters are just slightly more popular). Saltwater undergravel filters are identical to those used for freshwater aquariums. Undergravel filters are biological filters which rely on bacterial colonization. Simply put, these filters consist of a panel with many holes, which covers the bottom of the aquarium, a filter media, several (generally 4 to 6) uplift tubes, and an air lift or power pump. A general diagram of this filtering system can be found here.

As you can see in the diagram, the filter media and filter panel sit about 1/2 to 1 inch above the bottom of the tank. The substrate of the tank, or filter media, is located just above the filter panel. Aquarium water flows in the direction of the arrows. The air lift causes the aquarium water to flow down through the filter media and panel, where the actual filtering occurs, and then back up the uplift tubes. The air lift generally will have a an air flow control valve to adjust the rate of water flow.

Important Notes:

• Equal water flow through the uplift tubes is essential, otherwise some aquarium water may bypass the filtering media.

• Choice of filtering media is of great concern. A very fine media will provide a large surface area for colonizing nitrifying bacteria, but will require frequent cleaning to ensure efficiency of the filter. On the other hand, a larger particle sized filter media will be less likely to channel water flow, but requires additional mechanical filtration.

With regards to efficiency, undergravel filtering systems can work very well in many saltwater setups. They do require a bit of effort to clean occasionally, but provide reliable filtration which can lead to a very healthy aquarium.