Undergravel Filters Pros and Cons

Undergravel Filters Pros and Cons

I have had the honor of interacting with many experienced fish keepers, aquarium hobbyists, and aquarium pet store owners. What I have noticed in many such interactions is that the older and more experienced aquarists do not mind using undergravel filters.

In contrast, the overwhelming majority of new aquarists do not use undergravel filters; they use outside filters. Moreover, many new aquarists do not even know about the existence of undergravel filters.

In my opinion, the difference is quite easy to explain. Undergravel filters were very popular in the past. For this reason, those who built their first aquariums some time ago know about them and have seen them work. This is why they do not mind using them.

In contrast, new aquarists have joined the aquarium hobby at a time when the filters are no longer popular. For this reason, most of them are not even aware of them.

In this post, I will share with you everything you need to know about undergravel filters. I will share with you the pros and cons of aquarium filters and other important information. 

By the end of the post, you will realize that while undergravel filters are an ancient mode of filtration, they are very effective for biological and physical filtration. 


  1. Undergravel filters are easy to install and operate 

Most undergravel filters do not have many parts. They are, therefore, very easy to install. Most of them are also set and forget machines. After installing them, you do not have to do much else to make them work. 

In contrast, power filters, canister filters and other types of modern filters have got several parts. They are, therefore, not very easy to install. Moreover, one cannot really consider such modern filters to be set and forget machines. This is because many of them have buttons for manipulating various functions and require frequent maintenance.

In brief, in terms of installation and operations, undergravel filters are better than many modern aquarium filters.

  1. Undergravel filters are not visible 

As their name suggests, undergravel filters are undergravel filtration systems. You are supposed to bury them in the gravel/ substrate. The fact that you bury them in the gravel/ substrate means you cannot see them. For this reason, if you install an undergravel filter, it will not affect the beauty of your aquarium. It will not make your aquarium look any different.

And while you will not be able to see it, it will silently go about its business sucking fish excreta, uneaten food, and detritus into its system and cleaning your aquarium every day. 

In contrast, many modern filters are visible, bulky, unsightly, and make a bit of noise. So if you want a filter that you will not see or hear, you should get a good undergravel filter.

  1. Undergravel filters are effective filters

Filters are installed in aquariums primarily to remove toxic fish excreta which includes ammonia. They also eliminate uneaten fish food and detritus. Undergravel filters are very effective physical and biological filters.

Most undergravel filters have a superior biological filtration capacity when compared to other filter types. In other words, they can remove toxic fish excreta better than other filter types. They have a superior biological filtration capacity because they become populated with beneficial bacteria much faster than other filter types. 

So if you are looking for an effective filtration system for your fish tank, you should strongly consider getting an undergravel filter.

  1. Undergravel filters are cheaper to buy and operate

Undergravel filters are quite simple. They are, therefore, easy to build. The fact that they are easy to build makes them cheaper than other more complicated filter types.

So if you are looking for a filtration system and you have a low budget, you should strongly consider getting an undergravel filter. However, you should also keep in mind that there are different types of undergravel filters on the market. Some of them are more expensive than others since they include extra features. 

Hence do not just assume whatever you find online or in your local pet store is the cheapest undergravel filter there is. Do a bit of research to find the cheapest but effective model if you are on a budget.

Undergravel filters are also cheaper to operate and have longer life spans.

  1. Undergravel filters are versatile especially when used with Powerheads 

If you do not have a lot of cash to acquire a fluid-moving pump, you should get an undergravel filter and a Powerhead. The undergravel filter will do the filtration work and the Powerhead will make it even more effective. 

A good Powerhead will push the water through your undergravel filter plates and guarantee better filtration. Moreover, it will move your aquarium water and ensure better aeration of your tank. This will provide your fish and other oxygen-dependent tank inhabitants with oxygen. 

Additionally, you can make your undergravel filter even better by placing carbons, zeolite, or other media on top of its plates to increase its filtration potential.

In summary, undergravel filters are very versatile compared to other filter types.


  1. Undergravel filters are not very easy to maintain

Like most filter types, undergravel filters require a bit of work to maintain. Unless, you frequently vacuum your gravel, move the gravel about, and occasionally thoroughly clean your tank, gunk will accumulate in the substrate/ gravel and under your filter’s plates. This will make your filter less effective and it shows that maintaining undergravel filters is not easy.

To be fair, it is not very easy to maintain most types of aquarium filters. To protect your undergravel filter and prevent it from losing its capacity to filter your tank, you should regularly clean and maintain your aquarium. Additionally, you should never overcrowd or overfeed your fish.

  1. Undergravel filters cannot be used with ‘diggers’

If you keep fish that dig the substrate e.g. gobies, cichlids, and so on, you should look for another type of filter. This is because when such fish dig, they affect the normal functioning of undergravel filters by creating ‘channeling’ problems in the substrate/ gravel. 

When they affect the normal functioning of undergravel filters, they make such filters ineffective. Thus, you may assume that your filter is working but it will not be working. This can lead to a toxic buildup of ammonia in your tank that will kill your fish if you do not detect it early enough.

So if you keep digging fish aka diggers, you should not buy an undergravel filter.

  1. Undergravel filters can ‘trap’ small fishes 

If you install an undergravel filter, your blennies, gobies, or Kuhli loaches can get ‘trapped’ in its filter plates. This is because the plates have spaces where small fishes like to enter and hide.

However, this is not really a big problem because most fish usually come back out especially when they get hungry. Moreover, by properly arranging your gravel you can make it impossible for your fish to get trapped in your undergravel filter.

  1. Undergravel filters do not work well with plants

If you install an undergravel filter, you cannot really plant your aquarium. This is because there will be too much circulation at the root of the plants and this will prevent them from absorbing nutrients properly. 

However, this is not a big problem because you can still grow plants such as Sagittarias, Vallisnerias, Crypts, and Swordplants by potting them in small clay pots.


Undergravel filters are old-school or ancient filters. They were really popular in the past but now there are filters that are more modern and more popular. This does not mean undergravel filters are no longer useful or effective. As I have shared with you in the pros, undergravel filters have some really impressive advantages. They are effective, versatile, and easy to install and operate.

However, as I have also shared with you, undergravel filters have got several drawbacks. The cons include the fact that they are relatively difficult to maintain and that they cannot work with aquarium plants except if the plants are potted.

So undergravel filters have got both pros and cons. By weighing the pros and cons, I think the pros outweigh the cons. This is because most of the cons can be mitigated.

So if you really want to use an undergravel filter, do it. It will work just like any other good aquarium filter.