An under-gravel filter is a device that is used to clean the water in a home aquarium. Like most tank filters, they work by using a pump to suck air into a filtration chamber, where solids and harmful bacteria are filtered out. The best undergravel filter is the one that offers efficiency, invisibility, a quiet-running pump, and a reasonable price. With that in mind, let’s take a look at our top five picks for the title of “best undergravel filter.”
1. Penn Plax Premium Under Gravel Filter System (20 Gallons)
This one is a good deal because it includes everything you need to get started. It even comes with a couple of nice air stones, meaning that this one can double as an aeration device. Unfortunately, the air hoses are mounted at the top of the lift tubes. This does work well, but it takes away from the invisibility factor.
We do like the fact that these lift tubes lock firmly in place with a twist. This makes it far less likely that they will come loose during operation. We also like the added biological and chemical filtration, as opposed to the physical filtration that is offered by most models.
- Complete kit
- Includes biological and chemical filtration
- Thick, sturdy bottom plate
- Lift tubes lock firmly in place
- Top-mounted air tubes
This is a cheap and simple version that offers the chance to get the job done with minimal fuss. Unlike our last option, there are no special features to unpack, just a slotted filtration box and a single lift tube.
Of course, it would be nice if this thing had a second lift tube. That would allow it to push a little more water and keep the water just a little bit cleaner. Still, it should work fine for the tank size for which it is designed. When it’s installed, this one is very easy to forget, and the head is designed to aerate the water without the use of an additional pump.
- Really easy installation
- Base is like a box
- Aerates without a pump
- Very low visibility
- Only one lift tube
You couldn’t ask for a simpler model than this, but it’s also made to be a little more durable than most. The base is like a box, very thick and hard. Thus, there is much less chance of hearing it snap when you try to remove it from the gravel.
Like option number one, this one has included an aeration system that functions by using the extra air generated from the lift tubes. By doing this, you can save some electricity by doing two jobs with a single device. However, there is one big problem here. According to the advertisement, this thing doesn’t come with a water pump! This is just a filter device, so you’ll have to buy the pump separately.
- Has a very strong filter
- Plastic is extra durable
- Can be used with a power head
- Requires buying a separate pump
This is probably the most heavy-duty item on our list, and it’s also the most versatile. This one offers a thick, heavy base consisting of multiple layers. Because these slotted plastic pieces lock together, you can use them to create a size and shape that is perfect for your tank.
It might take a little more time to get this one working because it’s a little more complex, but that’s a small price to pay. We would be willing to bet that a multi-layer filter like this one will not have to be cleaned as often as others.
- Extreme durability
- Multi-level filtration
- Can be customized
- Comes with tubes and stones
- A little more complicated to set up
5. Lee’s Pet Products ALE13200 Undergravel Fishbowl Filter
This is definitely the smallest and cheapest item on our list, and it’s a special-purpose product. As you can tell by its size and shape, this one is meant to be used in a fishbowl. It isn’t good for any other type of enclosure, but it does a good job when used as intended.
The little decorative plant is a nice touch, but the carbon filtration at the top of the lift tube is much better. While one offers aesthetic and visual appeal, the other offers a real improvement in water quality. This one really is perfect for the fishbowl, even though it’s ill-suited for anything else.
The filtering holes of this model are very small, which is definitely a plus when dealing with very small fish. You don’t want to take the risk of sucking your little friends against the bottom, where they will surely die.
- Perfect for fishbowls
- Very cheap
- Includes a decorative plant
- Carbon filtration included
- Only suitable for fishbowls
Now that we have taken a closer look at some good examples of under-gravel filters, let’s go over some basic information about these devices and how they work. After all, it pays to know what you are buying.
How Does An Under-Gravel Filter Work?
Like most other water filters, these devices work by sucking air through a filtration media. This is usually a foam-like filter that is inserted into the baseplate. The gravel acts as an additional filtration layer, so a lot of the grime will be removed before it even reaches the filter.
When the water is sucked through the filter by a pump, it is then pushed up a lift tube. An air pump is used to get the necessary lift, and gravity does the rest. If you position the lift tube correctly, you can create a stunning waterfall from nothing more than a pile of rocks around the lift tube.
Advantages Of An Under-Gravel Filter
There are several good reasons to go with a filter of this type. For one thing, these filters are much less visible than any other kind. Canister filters and HOB filters are far easier to notice, and that is probably the main reason for the popularity of this filter type.
When you have a less visible filter, you can create an environment that is more like that provided by nature. This will probably result in a little less stress for your fish, and will definitely result in a more attractive aquarium.
Under-gravel filters also tend to be cheap. This might seem strange at first, considering that these devices are less popular than some others. Usually, things that are strange or uncommon will cost more. However, this is a pleasant exception to the rule. The basic design of these devices is so simple that they can be manufactured at a very low cost. That, of course, translates into a better price for you.
These filters are also space savers. Because most of the device is located under the substrate, you won’t have to worry about making space. As everyone knows, most aquarium filters are hung over the side of the tank. This works well, but it requires you to put a notch in the lid of the tank. Under-gravel filters, on the other hand, allow you to put a solid top on the fish tank. For creatures like ropefish that are prone to climbing out of the tank, these devices offer a great alternative.
Here’s another problem with the traditional side-hanging filters: They are too dependent on the water level. Due to evaporation, all fish tanks will occasionally require you to add more water. The thing is, your HOB filter (the more official term for the standard device) is pulling water through a long wand-like tube that projects into the water. The strength of the pump will limit its ability to work when the water level is low. If the pump is allowed to run dry, it can be ruined altogether. Thankfully, under-gravel filters do not have this problem because they are located at the bottom of the tank (the one place that should never be dry).
Disadvantages Of An Under-Gravel Filter
There are only two significant disadvantages to the use of an under-gravel filter. First, there is the fact that you will occasionally have to clean the gravel. As we said before, the gravel acts as part of the filtration process, functioning as a pre-filter that takes some of the strain off the main device. However, there is a price on this convenience.
Every now and then, you will have to use a small suction device to clean the gravel. To do this, you place the large end in the tank and apply some suction to the tube to begin the siphoning process. Some devices are equipped with their own pumps, but you will probably have to use your mouth to get it started. Make sure you take the tube out of your mouth before you get a faceful of fish water!
Once the siphoning process has started, place the small end into a bucket for drainage. You will need to keep an eye on the bucket and empty when needed. Now, you just use the large end of the vacuum to stir and agitate the gravel. As you do this, debris and filth will be knocked loose and sucked into the vacuum. Obviously, you are losing water as this process goes on, so try to get it done as quickly as possible. If the bucket is getting too full, simply pull the large end out of the aquarium to stop the flow.
The other downside of this filter type comes from the relative lack of access. If a standard filter gets clogged or otherwise becomes inoperable, it’s not that hard to take it apart and clear the blockage. If the filter stops working and has to be replaced altogether, it will be a simple job. None of this is true for an under-gravel filter. You can’t access this filter without digging it out of the gravel, and that presents a risk of breakage. Gravel is heavy, and that weight can cause the bottom plate to snap as you try to lift it from the bottom.
There is one more small problem when you choose a filter of this type, although it won’t be a problem for all users. Some fish like to dig in the gravel, whether to lay eggs, hide from other fish, or just out of boredom. For example, the Tiger Shovelnose Catfish often likes to dig in the gravel, creating a nice little pit in which to hide. Of course, the Tiger Shovelnose Catfish is a very large fish, so you probably won’t put them in a normal-sized tank. If you are using an under-gravel filter, you will need to make your gravel layer much deeper to accommodate these habits. Some smaller fish could even become stuck to the filter due to the suction.
The under-gravel filter may not be the most popular choice for home aquariums, but they definitely offer some distinct advantages. In the end, it’s probably best to use these devices in a small tank, such as an isolation tank, breeding tank, or other special-purpose enclosure. When you start using this kind of filter in a larger tank, it starts to get expensive and maintenance starts to become impractical. However, you couldn’t ask for a better way to keep a small tank clean. We hope that our work has been helpful and that you will come back to read more of our expert advice.