Undergravel aquarium filter: Working, Setup & Methods of Filtration

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An undergravel filter that is well-known and provides the best biological filtration for your fish tank is also called an internal aquarium filter. The right or adequate aquarium air pump helps to achieve accurate and desired results.


You could also have the powerhead (water pump) and have it set well so the right amount of gravel is in the undergravel making it easier and fast in purification and filtration. This review article of the undergravel aquarium filter will help you understand how the undergravel filter works and also how to set the aquarium up.

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Working of the Undergravel Filter


The majority substance or residue resides beneath the substrate and thus it is only sensible when you put up the undergravel filter while setting up the aquarium for the very first time. Depending on the size of the tanker or aquarium you might have to put a plate at the bottom. On top of the plate comes the gravel substrate. This order helps the water flow and thus it can flow freely under the substrate. The plates at the bottom are connected by filter tubes and then rise up where the aquarium water is at the top and thereafter returns to the tank.

Powering the filter is pretty easy. There are 2 methods available

  1. By the air pump
  2. By the water pump ( powerhead)

Air pump

An air pump is used in a fish tank so that the air is pushed up the tube and the air bubbles can rise up to the top of the tube. The water is then pushed out with the help of air bubbles and due to this effect, the water goes through the undergravel filter to the bottom of the tank.

Use a check valve if you choose this route because it proves to be more efficient and helpful. All air pumps tell you the amount or number of gallons that they are rated for so be extremely sure that you buy an air pump that is adequate for your aquarium.

Powerhead (water pump)

The undergravel filters the water an by an effect and then draws it to the tube through the gravel down to the bottom of the tank. Not very different from how the air pump works.

The square foot of the Aquarium determines the powerhead you require to use. 60-90 GPH per square foot is an ideal rate for the powerhead installed. For a larger base say 16×30 inch you a powerhead that pumps 200-300 gallons per hour will be required.

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The cycle flow is like this no matter what is used to move the water. There is no change in the cycle. When an air pump has used the oxygen in the water increases, on the other hand, a powerhead or water pump is likely to move the water faster than normal and increases the number of gallons per hour.

Methods of Filtration in an Undergravel Filter

  1. Mechanical filter

Mechanically the gravel acts as a filter itself. As the water flows and falls on the gravel, all the large particles and gravel pieces are caught in by the substrate and this further allows the user to easily clean it.

You could use a siphon (python) in the aquarium during water changes to clean it with accuracy or use an aquarium gravel vacuum cleaner to ensure deep cleaning.

So although people might be reluctant to buy this undergravel filter thinking it is hard to clean, it turns out it is not as hard to clean as they thought. This filter is pretty simple to use and clean.

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  •  Biological filter

The other method is the biological undergravel filter method and this happens in a few places in the tank such as the gravel, the grates that are beneath the gravel,  bottom of the aquarium,  walls of filter tubes, etc. All these places cultivate some bacteria and then it aids in removing all the ammonia, nitrites and other residues as flowing water cycle is on continuously.

This filtration system is a good filtration system, especially for biological filtration. The other one i.e the mechanical system is okay for aiding in a mechanical way.

Along with that, a part can also incorporate some degree of chemical filter or chemical filtration and most of these aquariums should use it as an additional filter. This one will be with power, internal and Sunsun canister filter. This filter will be doing the majority of work in comparison to the other filters or filtration methods.

Some systems accommodate carbon inserts that help the water leave the tube. It’s completely alright if you plan to have something additional along with the advanced system since not many have this type of chemical filtration available.


If the only type of filtration you decide on using is the undergravel filter then it is highly recommended that you see to it that it has the chemical filtration component at the time of your purchase.


Undergarvel Filters Advantages and Disadvantages

  • Extremely inexpensive
  • Sucks up gravel and is fish sensitive
  • Optional methods of filtration are available like a mechanical filter or biological filter
  • The minimal chemical filter is optional
  • Free maintain especially without chemical/carbon filtration
  • Easy to maintain
  • Simple manual with steps to set up
  • If steps are followed, setting up is also easy
  • Initial steps to set up aquarium has to be followed and filter has to be put at that time
  • Does not exempt all type of substrate. Sand is not filtered
  • Needs additional filter. It alone is not enough for an aquarium
  • Air/water pump is optional.

Easy Steps to Setup the Undergravel Filter


 People have their own preferences while selecting the pump. Some like the air pump and some like the powerhead (water pump). The oy thing I’d like to point out is while setting up the aquarium make sure the tank and pumps are all well positioned and powered.

Assembling the undergravel filter is not such a big task, once you understand the steps to follow it is pretty easy. Connect the hoses of this filter with an air pump after you finish assembling the rest.

It is expected that this filter is placed first in the tank before the gravel or substrate is poured in the tank, this helps fulfill the purpose of the filter.

Around 1.5 – 3 inches of the substrate is the average recommended range although it depends a lot upon the size of your aquarium of course. It is generally recommended to stay closer to an inch and a half end of the range for approximately 10 – 20 Gallon fish tank filter.

Those aquariums that are around 100 gallons or more should have it closer to only 3 inches of undergravel filter gravel in the tank. There is no fixed measurement but people’s experiences tell us this is the safest to follow.


The undergravel filter is highly recommended if you plan to have an aquarium and are looking for a less maintaining aquarium having many fishes for the large volume of the tank. Also if you want an additional filter to perform any sort of biological filtration then this is the filter to go for.

How does an Undergravel Filter Work?


How to set up Undergravel Filter with Powerhead?



One Reply to “Undergravel aquarium filter: Working, Setup & Methods of Filtration”

  1. I have used undergravel filters for many years and love them. I have a 20 long, a 36 gallon bow front, and a 55 gallon tanks. I only break them down once a year. The water in them is always crystal clear and beautiful.

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