I feel undergravel filters are underappreciated and underrated. That may be due to a lack of proper understanding of how they work and maintain them.
Before the advent of modern filtration systems, aquarists in the ’80s and ’90s used to keep their aquarium healthy solely with undergravel filters. A lot of people do in recent times as well.
When properly used, it can deliver almost the same filtration, similar to high-tech filters but at much lower prices. With its straightforward mechanism, it lasts for decades and requires less maintenance.
Let’s walk through the process of knowing undergravel filters, their benefits, and how you can use them in your aquarium effectively.
I’ve also looked at the market and carefully chosen and reviewed the five best undergravel filters, just for you.
What is An Undergravel Filter?
Image source: moashowmanyfish
Undergravel filters are the most basic types of aquarium filters you can find. They were once the go-to filter among fishkeepers. However, because of their low price, durability, and filtration ability, they are regaining popularity.
You can’t imagine how simple an undergravel filter is. Undergravel filter is nothing but a rectangular plastic plate-type grating, sits at the tank bottom. The plate has many holes or slots.
A pipe called a lift tube connects uprightly to the plate at the rear end—the lift tube functions as an outlet that returns the filtered water.
Gravel or substrates work as filter media, remaining over the plate. To begin the water movement through substrates, you need an air pump.
Undergravel filters are best suited in aquariums less than 55 gallons. However, you can also use them in bigger tanks with the help of a powerhead.
Working Principle of Undergravel Filters
Image source: ecology.pnnl.gov
The plastic grid of the undergravel filter is placed right on the glass bottom of the tank. Over the plate, you need to put gravel or planted substrate.
Undergravel filters use the substrate in your aquarium as a filtering element to trap the debris. The large surface area of the substrates also works as a medium for beneficial bacteria to colonize
An air pump or a powerhead is required to create the suction for water circulation through the substrate.
Air pumps outlet tube with an air stone placed inside the lift tube. The pressure created by the air moves the water. Along the way, water gets filtered in substrate layers and cycles back to the aquarium from the top of the lift tube.
Water goes through nitrifying bacteria that colonize on the substrate layers, converting ammonia and nitrites to nitrates.
The lift tube usually contains an elbow; the elbow carries an activated carbon filter for providing chemical filtration.
Benefits of Undergravel Filter (You Should Know)
It’s incredibly cheap; you can get one UGF suitable for use in a 50-gallon tank for only 15-20 dollars. But if you think about the output you can get, it is much more worth than the money.
So, what’s the point of buying an expensive filter if you can get sufficient filtration at a much lower price.
Better Biological Filtration
UGF uses the substrate’s entire surface area for growing nitrifying bacteria; it delivers better biological filtration than any other filter.
Water has to pass the substrates before reaching the lift tube. Along the way, all the layers get well oxygenated.
Oxygen is a must for aerobic bacteria to colonize. Hence GOOD bacteria grow everywhere the substrates. The bacteria break down harmful organic wastes into innocuous substances.
You won’t get the biological filtration from the first day of using your filter; it takes time for bacteria to establish; therefore, you need to cycle your tank. Check my detailed article on how to cycle a fish tank in three different ways.
Advantage During A Power outage
Although power outages are rare, if it happens, your filters will stop working if they are electrically driven like a canister or power filter. However, you can run your undergravel filter running with a battery-operated air pump temporarily.
What If you don’t have such an air pump? Don’t worry; bacteria inside the UGF can keep your aquarium healthy for an extended period.
Minimize the feeding amount or do a little more water change during the critical time of a power outage.
The filter plate completely hides under the gravel. Only the lift pipe with the elbow and the air tubing is visible. You don’t have to compromise with the aesthetic appeal.
Lift tubes stay at the rear end of the tank. Lovely bubbles create a fantastic view. If you own a planted aquarium, you can easily hide the pipes behind the driftwoods or lush plants.
The maintenance requirement is very low; once bacteria colonize, they maintain a healthy ecosystem inside the aquarium.
They neutralize the harmful substances into a safer form. Simply vacuuming the gravel every one or two weeks is sufficient. You need fewer water changes; however, you have to clean the substrate and the plate rigorously once every 18 months.
Compatible with Other Filters
Most undergravel filters are designed for aquariums up to 55 gallons. For larger tanks, you need to double the filter and accessories.
Many aquarists successfully keep aquariums over 55 gallons with multiple undergravel filters.
Moreover, you can easily use another type of filter concurrently with UGF if you feel the necessity, such as for heavily stocked tanks or greater bioloads, where only undergravel filters are not sufficient.
Less Operating Cost
Once you establish the filter in your tank, you have virtually no cost to operate—only the electricity bill of the continuously running air pump or powerhead.
You don’t need to replace the filter media like power filter, sponge filter, or canister filter. The only filter element UGF carries carbon.
You don’t need to replace the carbon filter often; it doesn’t cost much when you have to.
Highly Beneficial to Planted Tanks
As I said earlier, because of better air-water circulation throughout the substrates, good beneficial bacteria grow. Planted substrates become the storehouse of healthy bacteria, which converts the organic wastes into inorganic forms.
They transform fish poop, leftover foods, dead plant matter, or anything like that into invaluable nutrients like nitrates, calcium, potassium, etc. You won’t need any added fertilizer for your plants to thrive.
Aquaponics also works on similar principles. Suppose you keep fish wastes in a chamber and aerates sufficiently. In that case, bacteria colonize and break down the trash into essential nutrients for plants.
Using the undergravel filter allows you to make a synergistic relationship between plants and fish. A self-sustaining mechanism will take care of your fish, plants, and the water chemistry in your planted aquarium.
In that way requires fewer water changes and less maintenance. Some aquarists use solely undergravel filters in their planted tanks.
Reliable and Durable
Undergravel filters are easy to use, easy to install, and at the same time reliable and durable. Gratings are made of plastics; they don’t break and degrade over time.
Without any moving parts, undergravel filters are incredibly reliable. The only moving parts are the air pump or powerhead; if you buy a reliable one, you won’t face any problem.
Easy to customize
To get better chemical filtration, you can buy some carbon or zeolite bags. Place on top of the plate and cover the chemical media with the substrates; when water passes through the chemical media, you’ll get the chemically treated water.
It is also possible to boost biological filtration by placing the filter floss or sponges over the plate underneath the substrates. This innovation will enhance nitrification.
Getting the proper water flow is also not a big problem. If you like gentle water flow, use an air pump; for more robust flow, replace the air pump with a powerhead.
Factors to Consider for Undergravel Filters
Sufficient Air/Water Flow
Since air water movement through the substrates is the sole mechanism on which undergravel filter works, you need to ensure sufficient circulation.
If the movement is too low, it can’t aerate the whole layer of the substrates. In that case, harmful anaerobic bacteria—which thrive in the absence of oxygen—will develop, which can be deadly for your fish.
In case of too high flow, it will break away the layers of the substrate.
Therefore, you need to find the perfect balance in air/water flow. Air pump and airstone is the most common option for moving the water. However, you can use a powerhead since it can transfer a lot of water than the air.
Selection of Substrate
Preparation and selection of the substrates are vital for optimum performance of undergravel filters.
The thickness of the substratum bed should be sufficient to trap the debris. A layer of at least 2 inches is good enough. If the media base is too thick or too thin, it may alter the filter performance.
Choosing the right substrate type is another important factor. If you use too fine a substrate, it may block the holes of the grating plate. If it’s too coarse, you may not get the filtration you would like.
The best substrates to use with an undergravel filter are gravel, clay gravel, pebbles, clay pebbles, coarse sands, or anything of suitable sizes that don’t dissolve in the water and won’t degrade over time.
Some of the Disadvantages
Inadequate Chemical Filtration
Although some undergravel filters incorporate carbon cartridges, they are often not enough to provide adequate chemical filtration. Some brands also don’t add carbon to their design.
Suppose you are serious about getting the chemical filtration. In that case, you have to customize your UGF with zeolite or activated carbon.
Not Popular as Stand-Alone Filter
Undergravel filters are not vastly popular as stand-alone filters; they are often combined with other filtration units, although they can be used as stand-alone ones.
The reason behind this is, Biological filtration systems become weaker as time passes. Debris presents in the water pulled down to the substrates; as the debris accumulates on the gravel or substrates, it hinders water circulation.
The reduced air-water movement will deprive bacteria to get the necessary oxygen. Good bacteria don’t survive in a low oxygen environment, eventually deteriorating the water quality.
To prevent substrate blocking, you have to clean the substrates using a gravel vacuum. Some users also use a secondary filter unit to remove solid wastes to prevent clogging the substrates.
When to Consider Undergravel Filter
Yes, you can consider undergravel filter when
- You are going to start a new aquarium.
- You have a plan to revamp your existing tank.
- You want a low-maintenance small planted tank.
- You need to supercharge biological filtration in your tank.
Effective biological filtration is vital to keep the aquarium healthy. Undergravel filters offer the best growth of nitrifying bacteria; hence they are popular among aquarists.
Undergravel filters are a fantastic fit as stand-alone filters for small planted tanks. More giant size tanks will need an additional filtration system; common practice is to use power filters.
A fully functioning undergravel filter is capable of keeping your aquarium water clean. If you notice the water parameters are going outside the safe range, do some water change.
Regular changing of water and maintenance will give your undergravel filter the best run.
How to Set Up Undergravel Filters
To set up an undergravel filter, you need an empty aquarium. Setting up is straightforward. Follow the simple steps outlined below.
- Unpack the filter, and place the plate on the glass
- Attach the lift tubes with the plate
- Fill the tank with the substrate and later on with water.
- If you use an air pump, connect the air pump outlet with the lift tube to create suction.
- For the powerhead, prepare the pump, and join it on top of the lift tubes.
You can also watch this nice video for setting up UGF in your tank.
Maintenance of Undergravel Filters
Like all aquarium filters, you need to clean the filter media; here is the substrate. Proper maintenance of the undergravel filter will ensure the best performance.
Substrates trap the debris; they accumulate on different layers of substrates. Over the time being, if the wastes block the substrates, it will lead to low air/water flow.
Reduced air/ water circulation will hamper oxygens reaching the beneficial bacteria. A dead spot can appear where the oxygen supply is low, forming harmful anaerobic bacteria. Also, The inaction of beneficial bacteria will lead to poor filter performance and low water quality.
If the substrate is not cleaned periodically, residues and other organic wastes, including harmful hydrogen sulfide, may build-up.
Few bottom feeders can help to keep the top layer of the substrates clean. Bottom feeders live on the food or waste that sinks at the bottom. Check the article on the best bottom feeders and choose from the list. Avoid species that tend to burrow the substrates.
Frequent cleaning of the substrate by a gravel vacuum will prevent waste build-up. Depending on the substrate’s condition and air/ water flow, you need to plan a thorough cleaning.
Another way of cleaning is to put the siphon tube inside the lift tube and try to suck the debris. Following this procedure will help you clean the accumulated waste under the substrates.
Every aquarium is different, and maintenance requirements will vary from tank to tank. A quick weekly or bi-weekly vacuuming will help keep the substrate clean rather than allowing waste to build up over a month. Also, along with this, a partial water change will keep your aquarium water parameters healthy.
However, as long as you don’t overstock and overfeed and own a planted aquarium, a monthly cleansing and water change will be sufficient.
How to Choose An Undergravel Filter
There are many variations of the undergravel filter. Some use a single plate, some use two or more interconnected but separate plates to cover the whole aquarium.
Measure your tank bottom surface dimensions and make sure you are buying an under gravel filter that fits in your aquarium or can be adjusted to get the desired size.
Most under gravel filters don’t include equipment that needs to power them. You have to buy separately, either an air pump or powerhead, depending on your aquarium demands.
If you have aquariums over 55 gallons, you definitely need a powerhead to generate sufficient water flow. Also, if you have thick gravel or substrates, you may consider buying a powerhead. Otherwise, an air pump of adequate power is enough to run the undergravel filter efficiently.
When you place 3 inches of gravel over the plate, you need at least 60 gallons per hour (60 GPH) flow rate from your pump to achieve effective filtration. So, buy an air pump or powerhead with enough power.
Check the article on the best air pump; follow the buying guide to buy one that meets your undergravel filter demand.
Undergravel filters are mostly biological filters, providing mechanical filtration, but chemical filtration ability is relatively poor. Few under gravel filters also have the option to add a media cartridge to chemically treat the water.
Undergravel filters are not an excellent option to use for dirty aquarium fishes, like goldfish. They work best with low to slightly moderate bioload.
You can keep goldfish, but you need to consider the biowastes they produce. In that case, you will need more frequent maintenance.
Whatever you buy, you always have a budget, although undergravel filters are not expensive. But don’t forget that you need to buy an air pump or powerhead along with the filter; those could be a bit costly.
However, choosing the under gravel filter is a good option for those on a limited budget.
Best Undergravel Filter
If you made up your mind already to buy an undergravel filter, you could read this section. I’ve reviewed the six best undergravel filters available in the market. Here, you’ll get an unbiased review of the filter units.
1. Penn Plax Premium Undergravel Filter System
Penn Plax’s undergravel filter is designed to use in a 5 to 55 gallons aquarium, available in five different sizes.
The unit consists of plates, lifting tubes, carbon cartridges, and air stones. Clips are included in the package to attach the plates securely. The lifting tube provided is extra large and easily adjustable to get custom filtration.
Carbon cartridges are added to ensure chemical filtration, removing odor and water discoloration. You need to place them at the elbow section of the lift tubes. Carbon cartridges are suitable for 6-8 weeks; after that, you need to replace them.
Highly porous air stone included with the package to use with the air pump. However, you need to buy the tubing and air pump separately. You can use this undergravel filter both in freshwater and saltwater setups.
The filter unit is easy to assemble; it’s a matter of only five minutes to do that. Overall, this is the best undergravel filter, in my opinion.
What I like
- Easy to install.
- Snapping the filter plates together is easy.
- Includes carbon cartridges and air stones.
- Suitable for freshwater and marine water tanks.
- Five different models are available.
- Lift tubes are adjustable and extra-large.
What I don’t like
- Doesn’t include an air pump and air tubing, which is needed to operate the filter
- Connectors of the filter plates are not robust, can break easily
2. Imagitarium Undergravel Filter
The Imaginarium undergravel filter is suitable to use aquariums ranging from 10 gallons to 29 gallons, and you can use this either for freshwater or saltwater tanks.
The filter unit consists of two grating plates; you don’t need to snap the plates together since they can effectively work side-by-side without being connected. You have to attach the two lift tubes with the plates with air extensions and air stones.
Carbon cartridges are also added. They are also compatible with other filter brands, making it easier to find a replacement. This filter functions best with gravel or coarse sand substrates.
You need little maintenance to keep the filter unit running; wash the gravel or substrates thoroughly once every 18 months. Other than that, routine gravel vacuuming (weekly or bi-weekly) will help keep the tank’s parameters in good shape.
Similar to other undergravel filters, it also doesn’t come with an air pump or powerhead.
What I like
- Low maintenance frequency
- Cheaper than other units
- Replaceable cartridges are compatible with other brands.
- Plates function side by side.
- Two carbon cartridges included.
- Comes with air cords and air stones
What I don’t like
- Only two sizes available
- No air pump
3. Lee’s Premium Undergravel Filter
Lee’s premium undergravel filters offer a wide range of sizes. They are made of special plastics which don’t split and crack. Durable plastic plates are most preferred by saltwater aquarists because they won’t degrade in marine or brackish water use. Obviously, you can utilize freshwater setups also.
The plates are pleated style; with this design, they can withstand the heavier weight and hold the substrates better than the flat style trays.
Either one or two plates come in the package depending on the models; plates are extra-large, reducing the number of plates required to fit in the aquarium.
Each plate contains two riser tubes and an additional port to add an extra line if you need it. You don’t need to connect the plates since they can work separately.
This undergravel filter unit works fine with the air pump. You can still use it with a powerhead or a canister filter.
Like all other undergravel filters on the list, this filter unit also comes with carbon cartridges. Still, no air pump is included in the package.
The only drawback is riser tubes could have been a bit taller. Because of the advanced design, the price of this undergravel filter is also higher than other brands.
What I like
- Extra ports to attach additional lift tubes
- Pleat style durable plates
- A lower number of plates requires
- Each plate can work separately
- Carbon cartridges included
- Effective both in freshwater and saltwater tanks
What I don’t like
- Relatively smaller lift tubes
- Higher price than other brands of similar size
- It doesn’t include an air pump
4. XMHF Aquarium Fish Tank Undergravel Filter Board
This filtration system comes with filter boards of 32 pieces so that you can fit easily in different sized aquariums. Filter plates are constructed in 08 layers.
Yes, you have to take the hassle to connect the small-sized plates to exactly match your aquarium bottom surface. Though, snapping the plates is fun and very simple.
This filter also includes air stones, air tubing, and uprise tubes set up with the plates. However, unlike other undergravel filters I reviewed, it doesn’t contain any carbon filter.
So, if you would like to get chemical filtration using your undergravel filter, I don’t recommend this one.
Using this undergravel filter, you also need to buy an air pump. A powerhead or a canister intake can also be used to operate the filtration unit.
What I like
- Customizable to use virtually in any size aquarium
- Includes air stones, air tubings, and lift tubes
- Not expensive
- Easy to assemble the plates
What I don’t like
- So many small-sized plates take much more time to fit together
- No carbon media included
- The air pump doesn’t come with the package
5. Aquarium Equip ISTA Undergravel Filter
This ISTA undergravel filter is built to use in 5.5 gallons aquariums; you can use it in a more giant aquarium, buying multiple units. When using it in a smaller tank, All you need to do is cut the extra parts to fit your aquarium.
The plate contains one riser tube and provides a vast surface area for maximum biological filtration. This filter unit is operable by both air pump and powerhead.
You can also connect the plate with a hang-on back filter to boost the mechanical and chemical filtration.
The lifting tube is easily adjustable, and the tube head’s advanced design reduces any unwanted irritating sound. You can also place the riser tube at your preferred position, not only at the rear left or right corner.
Airstone is included in the package, but some users mentioned that air stone’s quality is not good. Carbon cartridges don’t come along with the filter; therefore, no chemical filtration.
What I like
- Adjustable lift tube
- Possible to place the tube in a preferred location
- Can be connected with HOB filter
What I don’t like
- Carbon media is absent
- No air pump
- Low-quality air stone
I guess now you have a better understanding regarding undergravel filters, their benefits, how they work, maintenance, and how to get the best results using them in your aquarium.
Selecting which one suits your aquarium, I hope this guide will help you tremendously. I’ve also reviewed the 05 best undergravel filters; you can also easily pick one from the list.
My favorite undergravel filter is the Penn-Plax undergravel filter; they have five different sizes, reliable and effective.