Undergravel Aquarium Filter: Top 5 Most Effective Cleaners

Whether you have a 125-gallon reef tank or a 5-gallon betta tank, you need a filter system if you’re going to enjoy healthy, long-lived fishes.

How so? Well, all living creatures produce waste products. Those waste products, together with decomposing plant matter, leftover food, etc., kick off the nitrogen cycle in your tank. If the nitrogen cycle is not managed efficiently by a filtration system, the water quickly becomes a toxic soup of ammonia, nitrites, and nitrates, which will quickly cause your fish to become sick and die.

There are several types of filter systems that you can use and dozens of different brands and styles of filter units. So, which do you choose?

In this guide, we focus on undergravel filters. Read this article to learn how undergravel filters work, how to maintain one, and the benefits of this kind of system. But first, we’ve picked out five of the best undergravel filtration systems and reviewed them for you.

5 Best Undergravel Filters

Here are our five favorite undergravel filters, together with helpful reviews and the pros and cons of each one. Pick out your favorite, and click the in-text links for more information and to place your order.

#1 Imagitarium Undergravel Filter

The Imagitarium Undergravel Filter is suitable for use with both freshwater and marine aquariums.

The filters are made to fit a standard 10″ x 19″ tank of up to 10-gallons capacity and are most effective when used with gravel or coarse sand substrate. Two filter cartridges are included with the unit.

The unit consists of two slatted filter plates that sit underneath the substrate. The plates are connected to two up-tubes that come with extensions and air stones. Note that you will need to buy a separate air pump to go with the filter. You’ll need to remove the fish and contents of your tank once every 18 months or so to wash the filters and gravel, but other than that, the system requires no maintenance.

Although the unit does the job of keeping the gravel fairly clean, most users have an external filter, too, as that provides more surface area for beneficial bacteria.

What we like:

  • Ultra-low maintenance requirements
  • Low price

Room for improvement:

  • Doesn’t provide much surface area for bacteria
  • Separate air pump not supplied

#2 Lee’s Original Undergravel Filter

Lee’s Original Undergravel Filter comes in a range of sizes and is reasonably priced.

The single plate is made from very high-quality, durable plastic that won’t split or crack, and there’s an optional flow-through setup that you can use with a powerhead. The robust construction means that you can use this filter with both freshwater and saltwater tanks.

The filter is designed with two adjustable 1″ uplift tubes that provide good water circulation through the filter plates. Multiple filter plates make installation a simple and trouble-free process. Airline tubing and airstones are included with the pack, although some users report that installing a powerhead provides better water circulation through the tank.

What we like:

  • Easy to install
  • Low price

Room for improvement:

  • Separate air pump not supplied

#3 Lee’s Premium Undergravel Filter

Lee’s Premium Undergravel Filter is a one-piece system that comes in different sizes. Installation is straightforward, and for best results, lay the gravel sloped downward from the back of the tank.

In this premium version of Lee’s UGF system, the plate size is larger than other systems, meaning that you don’t need as many plates in larger tanks. Like the standard version of this system, the materials used are built to last and are suitable for use in marine tanks, as well as freshwater and brackish setups.

The filter start-up time is less than many traditional canister or box filters, and once the system is up and running, the water remains crystal clear and safe for your fish with only minimal maintenance required.

What we like:

  • Easy to install
  • Strong and robust materials
  • Minimal maintenance

Room for improvement:

  • Separate air pump not supplied

#4 XMHF Aquarium Undergravel Filter Board

This system comes with 28 small pieces of multi-layered filter board, making it easy to customize for different tank sizes. The material used is strong and robust, so it won’t split and degrade if used in saltwater or brackish conditions. The plates are extremely easy to clean too.

The filter plates are very easy to fit together, and the uplift tube, airline, and airstone are all included with the pack. However, as is the case with most UGFs, you will need to buy a separate pump or powerhead, depending on the size of your tank. Most people find that this UGF works best when used in combination with a regular, external canister filtration system.

What we like:

  • Easy to install
  • Strong and robust materials
  • Reasonable price

Room for improvement:

  • Separate air pump not supplied

#5 Penn Plax Premium Undergravel Filter

Penn Plax Premium Under Gravel Filter System – for 40-55 Gallon Fish Tanks & Aquariums

  • Undergravel filter system includes 4 filter plates (each measuring 11.5″ X 11.5″) with extra large 1 inch adjustable lift tubes.
  • Filter is suitable for most 40 and 50 gallon aquariums. Clips to hold each section securely together are included.
  • 2 carbon filter cartridges remove odors, and water discoloration by trapping the pollutants in the pores of the carbon.

The Penn Plax Premium Undergravel Filter is one of the most popular UGF systems on the market.

The system is suitable for use with 40 and 50-gallon tanks and comes with four filter plates, measuring 11.5″ x 11.5″ each, which are held together by strong clips. The system includes two extra-large one-inch adjustable uplift tubes, airline, and airstones.

You can use the system in both marine and freshwater tanks, and two carbon filter cartridges are also included to prevent water discoloration and eliminate odors. Overall, the system is easy to set up, and maintenance is quick and simple.

Some users have reported that the undergravel tray connectors are thin and fragile and can break quite easily, so do be sure to handle these with care when setting up the system.

What we like:

  • Easy to install
  • Reasonable price
  • Effective filtration

Room for improvement:

  • Separate air pump not supplied
  • Tray connectors are fragile and easily broken.

What is an undergravel filter?

An undergravel filter (UGF) is perhaps the most basic filtration system that you can use and has been around for many decades. A UGF is simply a rectangular plastic plate or grate that sits underneath gravel or coarse sand substrate. The UGF drags water down through the gravel, providing a mechanical filtration system that offers a very large surface on which beneficial bacterial colonies can proliferate.

UGFs are best suited for use in aquariums under 55 gallons, although they can be used in larger setups with the addition of powerheads. When compared with other filtration systems, the UGF is one of the cheapest.

How does an undergravel filter work?

Undergravel aquarium filters consisted of one or more flat, plastic plates that are perforated with slots or small holes. The plate is placed on the bottom of the tank and covered with gravel.

At both back corners of the plate are uplift tubes that are fitted into the plate via a circular slot. The top of each of these tubes extends upward, remaining underneath the water surface. Inside each tube are air stones attached to the lengths of the airline. A powerhead or pump at the top of the column pulls water up through the uplift columns together with bubbles created by the air stone, which in turn drags water down through the substrate.

The water passes over the fragments of gravel, providing dissolved oxygen to the nitrifying bacteria that live in the substrate and helping to power the nitrogen cycle, which keeps the tank water clean and safe for your fish. Compared with a standard box filter system, a UGF offers a much larger surface area for bacteria to colonize, theoretically making this form of biological filtration system extremely efficient.

Reduced efficiency

As the water is pulled through the substrate, solid waste is taken with it. Over time, the spaces between the fragments of gravel fill with particles of waste, reducing the flow of water and eventually compromising the efficiency of the biological filter. For that reason, most aquarists use a UGF in tandem with another form of mechanical aquarium filter to get rid of waste before it becomes trapped in the gravel.

Some UGF systems contain a chemical filtration element in the form of an activated carbon cartridge that is placed at the top of each uplift tube, but most do not. Unfortunately, these cartridges only last a few days before they need replacement if they are to remain effective. Also, the cartridges tend to compromise the flow of water through the unit.

Maintenance of a gravel filter

As mentioned above, the main drawback to using a gravel filter is that particles of waste eventually accumulate between the fragments of gravel, blocking the passage of oxygenated water over the bacteria and down through the filter plate.

So, in addition to carrying out partial water changes, you will also need to vacuum the gravel each week to get rid of fish waste and uneaten food. Every 18 months or so, you should remove the filter plates and get rid of any fish waste and other detritus that is trapped underneath. It’s also a good idea to swill the gravel through in tank water to get rid of any accumulated waste, being careful not to wash away beneficial bacteria during the process.

You may find that algae forms inside and outside of the uplift tubes, so you will need to clean them periodically, using a soft bottle brush.

Pros and cons of undergravel filters for aquariums

There are advantages and disadvantages to using a gravel filter for your fish tank. Here’s what you need to know before you go down this route and choose a UGF for your aquarium.

Aquarium Gravel Filters

The advantages …

Here’s what’s great about UGFs:

Easy operation and reliability

One big advantage of a gravel filter is that it doesn’t have any moving parts. Aside from a powerhead or pump, the UGF is uncomplicated and reliable compared with more complex systems. Unlike many canister or box filters, UGFs are extremely quiet with just the gentle hum of the pump or powerhead to disturb the peace.

Ease of maintenance

With a UGF, you have no messy filters to wash or change. All you need to do is vacuum the gravel each week, as you would with any other filter system.

UGFs are invisible!

When you’ve spent a lot of time aquascaping your tank, the last thing you want taking up space and spoiling the aesthetics is a clumsy internal filter. That’s not a problem with a UGF, as it’s invisible, apart from the transparent uplift tubes and streams of bubbles.

Excellent biological filtration

UGFs are by far the best system, as far as biological filtration is concerned. Effectively, the entire substrate forms the filter media, unlike the standard few square inches of media that’s offered by most standard systems.

Inexpensive to buy and operate

Unlike many more sophisticated systems, UGFs are cheap to buy and operate. Once you’ve bought the unit and a pump or powerhead, you’re done. There’s no ongoing outlay on expensive replacement filter media and cartridges, and very little can go wrong unless the pump fails.

Versatility

If you want to, you can customize a UGF. If you want a stronger water flow, you can choose a more powerful pump or powerhead.

You can also incorporate chemical filtration by filling a porous filter bag with Zeolite or carbon. Push some of the gravel to one side, put the carbon baggie on the filter plate somewhere out of sight, and cover it with a small amount of the substrate.

If you want to improve the biological filtration performance of the system, place a layer of filter floss over the filter plates underneath the substrate. That will give nitrification a real boost, and you can use it in a freshwater, brackish, or marine tank.

And the disadvantages …

Unfortunately, every system has its downsides, and these are the cons to using UGFs:

Difficult to maintain

Unless you make it a strict routine to thoroughly vacuum your gravel every week, you may end up with a build-up of gunk and fish waste underneath the filter plate and trapped in the gravel. And every 18 months or so, you really need to tear down your tank completely to give everything a thorough cleanout.

Diggers and burrowers

UGFs are not suitable for use in tanks that contain burrowing or digging species of fish. Diggers create channels in the substrate. Water flows down through the channels, causing an uneven water exchange across the UGF plates, which ultimately affects the efficiency and performance of the system.

Disappearing fish!

Some species of fish and invertebrates are adept at sneaking underneath the filter plates and vanishing. Usually, the fishy game of “hide and go seek” doesn’t last long, and the critters reappear at feeding time, oblivious to the fright they gave you!

Live plants struggle to grow

Some species of rooted plants struggle to grow over filter plates because of the increased water flow through the substrate. However, you can overcome that by using clay pots to hold your live plants and choosing floating species that extract the nutrients that they need from the water column.

How to choose a UGF

When selecting the best gravel filter for your tank, there are a few things that you need to consider:

Additional components

All UGFs need something to power them. If you have a small aquarium, you can use a simple air pump, but larger setups over about 55 gallons will probably require a powerhead. When the filter is placed underneath a 3″ layer of the substrate, the flow rate should be at least 60 GPH (gallons per hour).

You may also want to use additional chemical filtration media, as mentioned above, although some UGFs do include activated carbon filters.

Size

Before choosing a UGF, make sure that you measure your tank floor so that you buy the correct size. Some UGFs are made from one single plate, whereas others can be two plates or more, allowing for a certain amount of tailoring to fit tanks of different sizes.

Budget

No matter what kind of filter system you’re buying, you will need to set yourself a budget before you go shopping. Generally, UGFs are the cheapest kind of biological filter that you can buy, making them a good choice for those on a limited budget.

In summary

An undergravel filter system could be a good choice for you if you have a small aquarium, and you don’t want the aesthetics of your tank spoilt by an internal box filter system.

UGFs are a good choice if you are on a limited budget, provided that you’re prepared to spend time each week vacuuming the gravel to remove excess fish waste and general detritus. However, if you have a very large tank, we recommend that you use a combination of a UGF and an external canister filter to keep the water clean and healthy for your fish.

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