Undergravel Filter Setup Guide: Assembly and Pros/Cons (2024)

Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: May 6, 2024
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The upkeep of a thriving and joyful aquarium critically rests on having pure water. Consider the stark difference between inhaling fresh, clean air and a breath laden with pollution and smoke – the parallel between our necessity for a hygienic environment and the needs of our aquatic friends is indisputable.

Article Summary

  • Undergravel filters are a traditional and effective method for maintaining a healthy aquarium environment by reducing the build-up of harmful waste and bacteria.
  • They promote biological filtration by allowing beneficial bacteria to accumulate on the gravel’s surface, which helps remove harmful organisms.
  • While they have advantages, undergravel filters also have some disadvantages, such as the need for additional clean-up and limited chemical filtration.

Fish in the wild can usually rely on the natural filtering process of tides and water flow to remove waste and oxygenated water.

In contrast we home aquarists must consider the artificial accumulation of these potentially hazardous materials and rely on complicated, often confusing mechanical filtration systems to care for our fish.

Worry not, dear reader as we’ve gathered the best information on creating an easy undergravel filter setup that will keep your fish healthy for years to come!

What is An Undergravel Filter?

Undergravel filters are one of the oldest filtration methods and have been used successfully for many years to decrease the build up of harmful wastes and bacteria in the aquarium and lower the stress of deep cleaning.

Typical “UG” filters consist of filter plates, typically about two inches wide (also referred to as the ugf plate) that lie below the gravel bed on the bottom of the aquarium.

Lift Tube

At the back of this plate type filter is a lift tube which is designed to pull air towards the bottom, creating a vacuum as air bubbles back up towards the surface. This vacuum pulls filtered water down through the gravel and the filter plate, to be carried out via the lift tube.


This may sound a bit confusing, but suffice it to say that undergravel filters allow us to use a simple air pump to do a huge amount of work for our overall filtration system.

How Do They Work?

Undergravel Filter
Undergravel Filter (1)

An undergravel filter works by using air pumps to create vacuum, pulling free floating waste and bacteria out of the aquarium water. The gravel substrate acts as a filter media as water passes through, trapping particles too large to make it down through small holes within the gravel to the filter plate below.

A more recent advancement in aquarium technology is the power filter. A powerhead water pump acts by mechanically pulling the water in those lift tubes upwards, rather than relying on the less efficient water flow vacuum generated by older under gravel filters.

In fact, these filters can be efficient enough that they don’t even require a separate canister filter.

Why Get An Undergravel Filter?

There are quite a few good reasons to consider undergravel filters when considering the filtration system for your fish tank.

  1. Affordable Upfront Cost and Upkeep – Considering that a typical system is little more than an air pump and a filter, these systems are often cheaper and easier to maintain than other options
  2. Biological Filtration – As beneficial bacteria accumulate on the surface of the gravel, they act to further filter out more harmful organisms
  3. Aesthetics – Undergravel filters are low-profile and are less likely to disrupt the natural beauty in your fish tank
  4. Compatibility with Other Filters – Undergravel filters make an excellent addition to other setups, such as a hang-on-back, or hob filter.
  5. Longevity – The simplicity of undergravel filters, along with their ease of cleanup can mean that you can keep one in your tank for the lifetime of some fish
  6. Customizable – The availability of multiple types of system setups means that a gravel filter can become part of most any fish tank
  7. Beneficial to Plant Tanks – The beneficial bacteria and biological filtration fostered by an under gravel filter can help remove chemicals that can harm your beautiful plants or worse, generate oxygen depleted environments altogether!
  8. Substrate Aeration – Water circulation through the base of your aquarium means less buildup of harmful bacteria, and increased oxygen for beneficial ones


Working on your plant tank? Consider the effect of air stones in CO2 levels before adding them to the tank if using an additional injection system.

Just remember that this will require more airline tubing between the air pump and stone (Skomal).

Disadvantages of An Undergravel Filter Setup

Unfortunately in most instances, undergravel filters cannot be the entirety of your aquarium filtration setup. There will be the need for additional cleanup as debris accumulates which can mean extra time spent vacuuming or manually removing pieces that are too heavy for the filter.

Saltwater aquariums with coral, also known as reef tanks, in particular can be a difficult match with a gravel system as the stand alone filter as the difficulty in cleaning around coral and large rocks poses a problem.

Air Stone

The air pump component of most under gravel filters can be obtrusive when running at max level, creating excess noise and visual disturbance. Consider an air stone to disperse those pesky bubbles!

Additionally, most undergravel systems do not include much by way of chemical filtration, meaning there is a possibility for an over-buildup of harmful sulfides and nitrates. This can be corrected by adding a carbon pre-filter unit to the lift tubes.

Carbon inserts are a great way to boost the power of any filter in your aquarium!

When to Consider Undergravel Filter

Penn Plax Premium Under Gravel Filter System
Penn Plax Premium Under Gravel Filter System

For a fish-only aquarium with proper air and water flow (possibly with the addition of an air stone to disperse air through the tank,) a gravel filter can make an excellent choice.

In any first-time tank setup, an under gravel filter can make for an easy to understand and setup system that when properly installed leads to lower maintenance and long-term stress for the aquarium owner, meaning more time to simply relax and enjoy!


An under gravel filter is greatly affected by substrate selection. Typically, this means using a finer gravel covering on top, with a coarse gravel layer beneath to best foster biological filtration.

How to Choose An Undergravel Filter

There are several factors to consider when choosing an appropriate filter for your tank:

  1. Aquarium Size – For a tank with a larger surface area, an under gravel pump and air filter system may need to be bulked up with more than one water pump! Note that size is typically based on an empty aquarium, and you may need to consider additional space taken up by decorations and the fish themselves.
  2. Filtration Requirement – Larger aquariums with more fish (and thus more waste!) may need to consider more than just one under gravel filter, additional chemical filtration and an air pump. Always start by checking the water quality when determining the specific requirement for your tank.
  3. Additional Needs – Tank is low on oxygen? Consider adding another air pump or two! There is typically always something you can add to an under gravel system to balance the downsides. Air stones, an air pump, and even extra chemical filtration may need to be considered.
  4. Budget – While a typical under gravel setup is relatively affordable, make sure to note the overall plan for your tank before diving in. One unexpected extra component can quickly mean three or four more, adding extra complications to something that should be fun and rewarding!

How to Set Up Undergravel Filters

As mentioned previously, setting up an under gravel filter system is relatively easy. Select your substrate (in this case, gravel,) determine the appropriate amount of gravel to add, and pour on top of your filter plates. After this, turn on the water pump to the undergravel filter and you’re good to go!

Things can get more complicated when considering additional filter equipment, or different varieties of aquarium or environment.

Here’s a quick video on how to set up your undergravel filter

How To Set Up a Penn-Plax Clear-Free Undergravel Filter

When using a powerhead undergravel filter, it can be as simple as plugging the head onto the tube of the existing siphon tube attachment.

These extra devices greatly increase the air flow efficiency of the undergravel filter, but it must be remembered that powerheads provide no extra filtering in and of themselves.

Ponds and Undergravel Air Pump Filters

But what about ponds? Undergravel filters can absolutely be a great fit!

The main thing to consider with a larger outdoor setup is that natural debris such as leaves and sticks can’t be mechanically separated by the biological filtration of an undergravel filter and may need to be removed manually.


Be sure to eliminate the presence of dead-spots on the bottom of your undergravel filter by properly pumping air to the surface from the bottom of the “outdoor fish tank.”

Maintenance of Undergravel Filters

To keep your aquarium under gravel filter working at its best, provide the maximum amount of possible filtration, and avoid filter problems, there are a few steps to consider.

  1. Keep the gravel substrate free of excess large debris, including old food, sticks, and particulates
  2. Use a back filter, a type of water pump designed to flush water back through the under gravel filter and unclog it
  3. Take note of when you need to add more components to the system. An overworked undergravel filter can’t provide the amount of filtration it should!


As we’ve discussed throughout the article, an undergravel filter setup can make a great addition to any aquarium.

They not only provide an easy to set up and maintain filter, but can decrease the amount of potential harmful chemical filtration required thanks to the presence of beneficial bacteria within the gravel substrate.

Once again I’d like to thank you for reading this article, and if you’ve found the information useful feel free to share it with other fish enthusiasts!


  • (1) Undergravel Filter By Fred the Oysteri
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