Undergravel Filter

Undergravel filters are a type of aquarium filtration that is located beneath the substrate (or under the gravel), and using them avoids the need for a clunky filter hanging on the back of your tank.

Utilize an Undergravel filter

  • Use a coarse gravel substrate (no sand).
  • Gravel vacuum the substrate regularly.
  • Use enough filter plates to cover the bottom of the tank.
  • Cover the filter plate with 1-2 inches of gravel.

How to install an Undergravel filter

To install an Undergravel filter, you must start with an empty tank. The Filter is made up of a flat, rectangular plastic plate that will sit on the bottom of your tank.

There are uplift tubes attached to the plate for moving water using either an air pump or a powerhead water pump. The tube pulls water down through the gravel and under the plate, then back up the tubes.  This creates a water flow through the gravel that pulls waste down and allows for aerobic bacteria to grow through a biological filter. Waste and debris will fall through the substrate and under the filter plate. The debris remains under the plate and needs to be periodically removed by deep gravel vacuuming using a siphon.

Benefits of Undergravel filter

The most important feature of the Undergravel filter is that it transforms bad bacteria into good bacteria. It does this using a variety of items. Such as an air pump, lift tube, media cartridge, and biofilm. They do not provide any chemical filtration and can be noisy when using an air pump. However, when properly maintained, Undergravel filters are easy, inexpensive, and low maintenance for most beginner tanks. Betta tanks and other small aquariums work well using an Undergravel filter. They can be used with an air pump and air pump and air stone to provide low water flow for slow-moving fish, such as bettas.

How much gravel do I need for Undergravel filters?

To ensure maximum efficiency with your filters, you will need to make sure that you have at least 2 to 3 inches of gravel above the filter plate. The gravel should be of mixed grades, but make sure that you don't have anything so small that can slip under or through the grating.

Maintenance of Undergravel filters

With an Undergravel filter, you will need to clean the gravel regularly. The easiest way to do this is by using a gravel vacuum you can find at your local pet store or online.

This is necessary to prevent the gravel from accumulating too much debris which would cause your filter plate to clog and not allow enough oxygen water to reach the good colony bacteria bed. This will result in lower water quality.

Do you have to clean the Undergravel filters?

Undergravel filters do need cleaning to keep them running properly, if the dirt such it is not removed it will eventually slow the flow of water through the bed.

This reduces the amount of oxygen getting to the beneficial bacteria, leading to poor performance and a determination in water quality.