Finding The Best Undergravel Filter For Your Tank

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Undergravel filters were once much more popular than they are today but are still a relevant, attractive option for your next setup. They are nearly silent, easy to install, and can go months between needing to be maintained.

Modern units also have customizable options like chemical filtration additions and compatibility with power and canister filters that increase their potential! If you’re the least bit curious, then let’s look into the best undergravel filters on the market right now!

The Best Undergravel Filters of 2021

Undergravel filters are simple in design yet have been around for decades. During this time, manufacturers have had opportunities to refine and expand on the original layout. Each of these undergravel filters is the cumulation of this process and are the best models I’ve found in today’s competitive market!

Here are my favorite undergravel filters of 2021! 

• Lee’s 50/65 Premium Undergravel Filter   **Top Choice**
• Penn-Plax Clear-Free Premium Under Gravel Aquarium Filter
• Lee’s 15/20 Original Undergravel Filter
• Aquarium Equip Undergravel Filteration Bottom Circular Bar
• Aquarium Equip ISTA Undergravel Filter

Now that you know what’s coming, let’s take a moment to talk about why you’d want to use an undergravel filter!

What is an Undergravel Filter Good For?

Undergravel filters are perfect for aquarium setups where you want to maintain as minimalist an aesthetic as possible. Since the only visible portions are the twin tubes running along the rear corners of the tank, you can easily hide them with tall plants, driftwood, and other aquascaping components.

While they aren’t as powerful or versatile as a canister or power filter, they are less energy-intensive, less expensive, and need little to no adjustment once installed. An undergravel filter only needs cleaning every few months rather than biweekly or monthly, as other filters do. They are also as quiet as the air pump running it, which is usually silent, or nearly so. 

And the vast surface area they have thanks to the substrate acting as your filter means they have unmatched biological filtration capacity. Beneficial bacteria make the gravel in the filter their home. And by doing so, they consume loads of ammonia and nitrite, converting it to nitrate which is then removed by you during water changes!

My Top Choices for the Best Undergravel Filters

Lee’s 50/65 Premium Undergravel Filter

Lee’s Premium Undergravel Filter uses a single plate design versus two plates that meet in the middle. This design makes lifting the filter for maintenance easier since gravel won’t get trapped in between the plates. Fish also have a harder time burrowing under the filter this way. Sometimes a single plate design is more likely to crack, especially during installation. But the thicker, crack-resistant plastic of this model ensures this won’t be the case.

The chambers that hold your activated carbon are also quite generous and provide superior chemical filtration compared to other designs. However, the lift tubes don’t adjust, meaning you’re stuck with the standard configuration. This can make them unsuitable for shorter aquariums.

One aspect of this filter you might find frustrating is that the dimensions are fairly unusual. Aquariums with an 18″ x 36″ footprint are not common; a 50 and 65 gallon high comes to mind. The more common 30 and 40-gallon breeder tanks also use this footprint but the non-adjustable lift tubes sit too high in these tanks. Fortunately, Lee makes several models that fit aquariums from 10 up to 125 gallons in size, but it complicates the buying process somewhat. 

Penn-Plax Clear-Free Premium Under Gravel Aquarium Filter 

If you prefer a twin-plate style then the Penn-Plax Clear-Free Premium is a model to consider! Twin plates can be installed in tanks that are longer than the aquarium they are rated for but it’s best to choose the right sized model for good flow. You also have locking clips in the Penn-Plax design that prevent grains of gravel and fish from getting under the filter plates.

Unlike some of the other manufacturers here the Penn-Plax designs fit a narrower range of aquariums, from 10 to 55 gallons in size. While these are the most common sizes people buy, folks interested in filtration for larger tanks should look into Lee’s models.

Twin high-pore air stones provide aeration when an air pump or powerhead is attached and drive flow through the two activated carbon chambers. Each chamber sits at the peak of an adjustable lift tube that allows you to customize how water flows throughout your setup.

Lee’s 15/20 Original Undergravel Filter

Lee’s offers not only a Premium but has an Original model still in production worth a look! One thing to consider is that the Original doesn’t have a third port to attach another lift tube for extra filtration. Instead, you’re using the traditional twin-lift tube design. However the Original does have adjustable lift tubes included so you can customize not only the height but how water moves throughout the tank with ease!

Like the Premium the Original uses a single section of rigid, crack-resistant plastic. This design simplifies both setup and undergravel filter maintenance. The design of the activated carbon chambers is noticeably different from the Premium model but works just as effectively at screening the water column for dissolved organic matter.

Lastly, the 24″ x 12″ footprint makes this perfectly sized for a 20 gallon “high” aquarium; one of the most commonly sold tanks out there! And if you prefer using a powerhead to create flow through the unit this model includes an optional flow-through setup for compatibility!

Aquarium Equip Undergravel Filtration Circular Bar

Anyone familiar with standard undergravel filters will instantly find the Undergravel Filteration’s design intriguing! Rather than flat plates it uses a series of slotted tubes that run throughout your substrate. Water is pulled into the slots and runs through the tubes before being expelled from the single black plastic lift tube. Aquarium Equip makes several models that fit aquariums from 10m to 55 gallons.

The simple, straightforward design can be attached not only to air pumps and powerheads but power and canister filters as well, adding to their mechanical and biological filtration potential! And since it isn’t using a plate design it’s easier to rebury within the substrate if you need to remove the unit.

Something to consider with this design is that you only have one lift tube, which reduces the total flow and current generating capacity of this model. The tube is also black, rather than clear plastic, which can be harder to disguise in an aquascape. 

Aquarium Equip ISTA Undergravel Filter

The Aquarium Equip ISTA Undergravel Filter is another cleverly designed unit that departs from the traditional styles seen on the market! The first thing you’ll notice is the raised platform design. This style of undergravel filter allows extra space for debris to collect and eases the flow of water from the plate to the lift tube. Traditional undergravel filters can become clogged if not maintained properly, reducing flow and the overall filtration capacity of the unit.

But there are a couple of trade-offs to consider with this model. The first is that it doesn’t include activated carbon cartridges; in fact, it has no place anywhere for carbon inserts. This means you have no chemical filtration capacity unless you run a secondary unit alongside the ISTA. 

Another consideration is that this uses a single lift tube. While the raised platform increases flow, the single tube doesn’t provide as much flow as a twin-tube design. But for aquarists with more powerful air pumps or powerheads driving it, this may be a good trade!

Which Undergravel Filter is Best for You?

As we’ve seen, the various undergravel filters available online offer a diverse range of features and are all highly affordable and effective! But the filter that most stands apart from the rest are undoubtedly those in the Lee’s Premium Undergravel Filter line!

The durability of the plastic used is better than that of Penn-Plax and other models. And the single filter plate design eases maintenance and prevents burrowing fish from getting under the unit. We also not only get an optional port for a third lift tube but activated carbon chambers of generous size attached to the included tubes. I do wish the tubes were adjustable but you can’t have it all!

Undergravel Filters and Your Aquarium

Do I Need Other Items to Run an Undergravel Filter?

Yes; unlike a power or canister filter, most undergravel filter setups don’t include a pump, powerhead, or other source of water flow to keep it running. On the plus side, this means that you can choose precisely the pump or powerhead you want rather than being stuck with whichever the manufacturer provides.

Many, if not most, undergravel filters also have activated carbon cartridges that provide chemical filtration alongside the mechanical and biological filtration capacity of the unit. Activated carbon allows the unit to remove dissolved organic molecules that feed algae and decay into ammonia and other toxic chemicals. You will need to buy replacement activated carbon but fortunately, large containers are very affordable and easily found at your local pet store!

Undergravel Filter Maintenance

Maintaining an undergravel filter is both positive and negative in many ways. The positive side is that you don’t need to service them very often. Once waste is pulled into and under the gravel it will slowly decay and (mostly) remain there for months at a time. The activated carbon holders should be changed out biweekly. But this can be done in less than five minutes; simply toss out the old carbon, fill the chamber with fresh carbon, and then rinse it before re-attaching it to the filter. Rinsing is important because it washes away the fine charcoal dust that would otherwise irritate the gills of fish should they breathe it in.

The downside of servicing an undergravel filter is that it can be extremely messy once it’s time to do so. How messy depends on how long you wait before doing a cleaning and how heavy your fish bioload is. If you have a lightly stocked aquarium, your unit may only need to be serviced once every 6 months, or even never if the bacteria in the gravel can decay waste products quickly enough.

But that’s rarely the case in an aquarium; usually, you’ll have to lift up the plate, exposing your aquarium water to an influx of trapped waste and organic matter. One needs to be very careful, otherwise you may need to do a complete water change to remove all of the suspended debris.

The simplest way is to turn off the undergravel filter’s pump, and then use a gravel vacuum to suck up the trapped debris through the filter mesh. Here’s a video demonstrating just how to do so:

This is best for tanks where the trapped debris hasn’t gelled into mulm. Mulm can form loose clay-like layers that may be too thick to fit back through the undergravel filter plates. This usually happens if you wait too long to do undergravel filter maintenance. 

Mulm isn’t any worse than regular poop; it’s simply a mixture of waste and bacterial colonies but you still don’t want too much of it floating around your tank. You may have to lift up the plates entirely in this case, which will wreck your aquascape but allow you to clean underneath.

When Should I Not Use an Undergravel Filter?

Undergravel filters are versatile, affordable, and effective, but they aren’t great for every aquarium setup. If you have any of the following fish or plants, I’d recommend against using an undergravel filter.

Aquariums with Live Plants in the Substrate

Live plants present a problem for undergravel filter users: plant roots hate to be disturbed. But they will eventually make their way on and through the filter plates as the plants establish themselves. When you do maintenance on the filter you’re almost certainly going to disturb or uproot the plants, which causes them immense stress.

One benefit is that the filter pulls loads of organic debris straight to the roots for plants to feed on. Ammonia, nitrite, and nitrate are all important nutrients that boost their growth. But the roots will quickly be too much of an obstacle for it to be worth doing. I recommend epiphytes (plants that grow on hard surfaces) like Anubias and Java Moss if you want both an undergravel filter and live plants!

Aquarium with Digging or Burrowing Fish

If you have fish that dig like cichlids or ones that burrow like loaches, you’ll want to avoid an undergravel filter. These sorts of fish will create pits in the substrate that interfere with the flow and filtration ability of the unit. And burrowing fish will eventually work their way under the plates entirely, which not only disables it but creates a new problem: catching the fish. Speaking from personal experience it can take a long time to catch a loach that doesn’t want to come out of your undergravel filter and it usually ends with you making a huge mess of your aquascape.

Overstocked Aquariums

Overstocked aquariums are the last place I would use an undergravel filter. The unit will remain functional so long as you perform regular gravel vacuums and water changes. But if you slack, the gravel will quickly fill with waste from the fish, which looks very unattractive once it begins to build up. This also increases your chances of thick mulm forming, which often means you’ll have to tear up the bottom in order to get it all out. A canister or power filter, coupled with regular water changes, is a much better option for an aquarium that has a lot of fish.

Conclusion

As you now see, undergravel filters are effective in the right circumstances and one of the best ways to keep a tank clean! They are easy to hide, simple to operate, and need less maintenance than power or canister filters. Just keep them away from live plants, overstocked tanks, and digging fish and you’ll be just fine!