If you’ve been looking for a way to improve the biological filtration in your tank without taking up much space, an under-gravel filter may be just what you’re looking for.
Undergravel filters are exactly what they sound like, a filter seated below the gravel or other large substrate. They work by pulling water through the substrate, using the surface area of your substrate to colonize beneficial bacteria. Some undergravel filters use carbon filter cartridges while others do not, so they are always biological filters but they are not always chemical filters.
Undergravel filters work best in conjunction with another type of filtration that can catch large particles of waste and detritus. This will help reduce the build-up of waste products underneath or inside of the undergravel filter. They work best in tanks less than 55 gallons, but there are a few that make great additions to larger tanks.
We’ve taken care of these product reviews to make it easier for you to pick an undergravel filter that will work best for the size, shape, and waste needs of your tank!
A Quick Comparison of Our Favorites
|Best Overall||Penn Plax Premium Under Gravel Filter System||
|Best Value||Imagitarium Undergravel Filter||
|Premium Choice||Lee’s 40/55 Premium Undergravel Filter||
|Aquarium Equip Undergravel Filteration||
|Aquarium Equip ISTA Undergravel Filter||
The 6 Best Undergravel Aquarium Filters – Reviews 2021
1. Penn Plax Premium Under Gravel Filter System – Best Overall
The Penn Plax Premium Under Gravel Filter System is the best overall undergravel filter we reviewed. This filter is available in five sizes for tanks from 5 to 55 gallons. Checking the measurements of the product versus the measurements of your tank before purchasing is wise to make sure you get a filter that is the right size to filter your tank and physically fit into your tank.
This filter system includes filter plates that snap together easily, lift tubes with adjustable height, high pore air stones, and your first set of carbon filter cartridges that are made to last 6-8 weeks. This undergravel filter system is easy to set up and the filter cartridges are easy to change, making maintenance easier. The slats in the filter plates in this set are made to work with gravel, so they are large enough to allow adequate flow without the substrate dropping into the filter.
This kit does not include an air pump or airline tubing, so you will need to purchase these items separately. Make sure to purchase an air pump that can handle the tank’s volume. A mini air pump isn’t going to cut it for a 50-gallon tank.
2. Imagitarium Undergravel Filter – Best Value
For the best undergravel aquarium filter for the money, we like the Imagitarium Undergravel Filter. This filtration system is available in 10-gallon and 29-gallon sizes and can be used in freshwater or saltwater tanks, although it is not reef safe.
This filter kit includes two plates that snap together, but the plates don’t need to be snapped together for the filter to work effectively because the plates can function side-by-side without being connected. This kit also includes lift tubes, air stones, and replaceable carbon filter cartridges.
This undergravel filter is extremely cost-effective and accepts filter cartridges from other brands, making it much easier to find replacement cartridges when needed. This filtration system does not include airline tubing or an air pump.
3. Lee’s 40/55 Premium Undergravel Filter – Premium Choice
The best premium undergravel filter is Lee’s 40/55 Premium Undergravel Filter, or any of the Lee’s undergravel filters. These filters are available in six sizes from 10 gallons all the way up to 125 gallons. This filtration system is freshwater and saltwater safe.
Lee’s Premium Undergravel Filters are unique because they consist of one high-quality plastic plate that is made to resist cracking under the weight of an aquarium substrate. The installation is easy and only having one plate takes one step out of the process. This kit also includes two lift tubes that are not adjustable, air stones, and replaceable carbon filter cartridges. These cartridges are not able to be fully removed from the filtration system for people who prefer to not use them.
This system will accept parts from other brands and as a bonus, it’s black, so it will blend into more substrates better than other undergravel filters that are white or blue. Air pump and airline tubing are not included.
4. Aquarium Equip Undergravel Filteration
The Aquarium Equip Undergravel Filteration kit is a little different from the normal undergravel filter. This consists of a set of tubes and elbows that sit under the substrate and allow water to flow through them. This filtration system is available in 10-gallon and 55-gallon sizes. It is freshwater, saltwater, and reef safe.
This type of undergravel filtration system can be used with air pumps or connected directly to other filtration systems, like canister filters. It is not made to function as the sole filter of an aquarium. This kit only includes the plastic tubes and elbows and does not include an air stone, air pump, or other types of equipment.
A nice benefit of the Aquarium Equip Undergravel Filteration system is that it can be used with sand substrate, unlike most undergravel filters. Ideally, it should be used with a larger substrate, like gravel, to improve water flow.
5. Aquarium Equip ISTA Undergravel Filter
The Aquarium Equip ISTA Undergravel Filter is cost-effective but only available in one size for small tanks up to 10 gallons. This undergravel filter can be used in freshwater and saltwater tanks.
This product is somewhat different from most undergravel filters because it does not sit flat on the bottom of the tank. Instead, the plate is attached to short legs that raise the plate off the bottom, but there are no sides to prevent waste and substrate from getting underneath the plate, which can lead to waste buildup. The plate can be cut to fit oddly shaped tanks and will still function as long as the lift tube can still be attached. The kit also includes an adjustable height lift tube and a plastic air “stone”. This filter is best used with gravel.
This undergravel filter can be connected to an air pump as well as other filtration systems, like canister filters and HOB filters. This filter will not function adequately as the sole filter in the tank and does not have carbon filters.
6. uxcell Plastic Fish Tank Undergravel Filter
The uxcell Plastic Fish Tank Undergravel Filter is a cost-effective product for various sizes of tanks. This kit comes with 24 small plates that can be connected to form a larger plate. They can be put together side-by-side or end-to-end.
This kit includes the 24 black plastic plates, a lift tube, and an air hose line attached to an air stone. It does not include an air pump or full-length airline tubing. While the plates are black, the joints of the lift tube are white, making this noticeable in an aquarium.
This system can be connected to an existing filtration system like HOB or canister, but it should not be used as the sole form of filtration. It does not have any type of carbon or other chemical filtration.
|When to Use an Undergravel Filter||When to Use a Different Filter Type|
|When cycling and establishing a new aquarium||In tanks with fish that dig regularly|
|After a cycle crash due to cleaning or chemicals||In a planted tank with well-established or sensitive plants already in place|
|When you want to improve the functionality of your current filtration system||In a bare-bottom tank|
|In a low bioload or understocked tank||In an overstocked tank|
|In a tank with gravel or pebble substrate||In a tank with a sand substrate (tube-based undergravel systems are the exception)|
These reviews cover more than one type of undergravel filter, giving you options for what might work best in your tank. The Penn Plax Premium Under Gravel Filter System was our pick for the best overall product for its high-quality and high functionality, but the Imagitarium Undergravel Filter has a similar appearance and function for the best value. For a premium product, check out the Lee’s 40/55 Premium Undergravel Filter. This product has a clean, simple design made from high-quality materials.
All of these products have the potential to work well for you, but only you know what your ideal vision for your tank is. Undergravel filters aren’t without their issues, but they make an excellent addition to an established filtration system. They can also be used when cycling a new tank to speed up the process of beneficial bacteria growth. Undergravel filters are easy to set up and easy to use, making them beginner-friendly, so don’t let their unusual appearance intimidate you.
Featured image credit: Krysja, Shutterstock