How Does An Undergravel Filter Work? | Aquascape Addiction

How Does An Undergravel Filter Work?

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Wondering how does an undergravel filter work? this post covers everything you need to know including some of the best options for your tank.

How Does An Undergravel Filter Work?

Without a doubt, the most important thing that you need for any aquarium is a water filter, that is of course besides the fish themselves. A good filtration unit is absolutely necessary for keeping your aquarium clean and for keeping your fish healthy. That being said, there are many different kinds of filters out there which you can choose from. One of those types of aquarium filters is the undergravel filter, an easy to set up, affordable, and highly efficient filtration method that you will definitely be happy with. In this post we answer the common questions such as how does an undergravel filter work, set up and some of the best options to consider so let’s dive into it.

What Is An Undergravel Filter?

An undergravel filter is a really neat innovation when it comes to aquarium filters. An undergravel filter is a type of aquarium filter where the gravel, which is your substrate, is used as the primary filtration method. The filter will usually consists of some kind of grate to keep the gravel from touching the bottom of the aquarium, a pump to draw water in, a pump for air, power heads, and sometimes they do even come with their own filter media. However, by in large, the gravel is what is used as the primary filter media. Keep in mind, this does mean that the gravel itself will require some cleaning every now and then.

How Does An Undergravel Filter Work?

An undergravel filter is actually a pretty simple type of filter and the way it works is about as uncomplicated as it can get. First of all, there is a grate located under the gravel to stop the gravel from touching the bottom of the aquarium, which lets water flow under it. There is a water pump and a power head which draws water through the gravel, with the gravel working as a biological filters as well as a mechanical filter. To move the water under the gravel there may also be an air pump involved.

There is then a power head and water tube which pumps the clean water into the tank. Also, there are air pumps involved which blow air bubbles up from the bottom into the lift tube in order to lift the fresh water into the top of the fish tank. It all kind of acts like a water cycle because water gets drawn in through the gravel and the clean water gets shot out the top, which then in turn causes more dirty water to filter through the gravel.

If you need help with how much gravel your tank needs then this post should help you out.

How To Set Up An Undergravel Filter

Installing an undergravel filter in your aquarium really is not that hard. First of all, assemble the filter according to the instructions of the specific undergravel filter you get. Before you put the filter in the tank, make sure that all of the gravel is very clean, then place the filter grate along with other necessary components in their proper place. You need to make sure that the grate covers the whole floor area of the tank. After you have done this, simply put the gravel onto the grate and make sure that it is evenly distributed.

What We Think Is The Best Undergravel Filter

If you want a great undergravel filter for your aquarium, check out this model by Lee aquarium specialists.

Lee's 40/55 Premium Undergravel Filter

This is a fantastic undergravel filter choice to go with. It features large plate size in order to reduce the number of plates that are needed to cover the bottom of your aquarium. This thing uses state of the art power heads, air pumps, and water pumps in order to effectively suck water through the gravel and pump clean water back into the aquarium. This is a highly effective undergravel filter with a very strong UGF plates that are extremely durable and it works great for both fresh water and salt water aquariums.


  • Very durable.
  • Powerful filtration unit.
  • Large plates for big coverage.
  • Comes with everything you need.
  • Easy to set up.
  • For salt water and fresh water.


  • Attaching extra filter media is a challenge.

Check the price at Amazon

3 Other Options To Consider

Everybody is different and has different tastes, so we know that you may not be a big fan of the first undergravel filter which we mentioned above. To give you a little diversity we also have another 3 great undergravel filter options to go with.

1. Undergravel Filtration Bottom Circular Bar

This is a pretty good undergravel filter to go with. This thing features a unique snake like design that consists of 3 horizontal tubes which suck in water through the gravel, filter it, and disperse it back into the aquarium with 1 vertical tube. This filter is ideal for smaller tanks with fairly large gravel. This is a pretty good filter to use for smaller tanks.


  • Effective filtration unit.
  • Good for smaller tanks.
  • Works for salt and fresh water.


  • Does not come with necessary grates and pumps.

Check the price at Amazon

2. Aquarium Equip Under Gravel Filter

This is a very simple yet effective undergravel filtration unit. This thing comes practically assembled, it is powerful and effective, and it works really well too. This model is ideal for all types of water and different types of aquarium. However it is somewhat small. This makes it ideal for smaller aquariums, while larger aquariums will require several of them for effective filtration.


  • Powerful filtration.
  • Sleek design.
  • Great for all aquariums.
  • Does not require much space.
  • Comes almost totally assembled.


  • Not ideal for larger aquariums.

Check the price at Amazon

3. Undergravel Filteration Bottom Circular Bar

Yet another good undergravel filter option to go with is the Aquarium Equip Undergravel Filtration Unit. This thing is just like the first option that consists of circular horizontal tubes which suck in water through the gravel, cleans it with the gravel and then disperses it back into the aquarium. This thing works for both salt water and fresh water tanks, plus it is ideal for most tank sizes.


  • Ideal for all aquariums.
  • Very powerful.
  • Easy to set up.
  • Effective filtration.


  • Not that easy to set up.

Check the price at Amazon

How To Clean An Undergravel Filter

These things may seem really hard to clean because they are covered with the gravel (your substrate), but you don’t actually have to remove the gravel to clean them. They don’t involve as much work as other filters, in terms of cleaning the filter itself at least. Since under gravel filters do a lot of the work by sucking the debris into and through the gravel, cleaning the gravel is the hardest part.

Simply use a syphon and gravel vacuum in order to suck the debris out from the gravel. After you have done that, you can actually reverse the flow on the filter to push any gunk, debris, and clogs back through the filter and up through the gravel, all of which can then be sucked up with the vacuum (here are our top 5 vacuum picks). Other than that, just wash out the tubes and pumps just like you would with any other filter.

You can also clean gravel without using a Siphon which we have covered here in a step by step guide.


The bottom line is that undergravel filters make for some really great filtration units (we have done a detailed comparison here vs power filters). They are quite powerful, they are easy to use and set up, and they work pretty darn well too. Remember, no matter what filter you get, your fish will appreciate a good undergravel filter without a doubt.