Aquarium Sponge Filters. What They Are and How They Work – The Guide

sponge filter in a fish tank

For some reason, people overlook the aquarium sponge filter and go for a more complex system such as those fancy ultraviolet sterilizers for fish tanks, which not always works better than the simple sponge.

Although sponge filters have been around for so many years, only a few know or have an idea of what they are, what they do and how they work.

The #1 reason for this apparent neglect may be because they appear unnecessary and very simple to many. But is it, really?

Now, here’s the thing. This type of filter, for the price tag that it comes with, has an incredibly high quality/price ratio. But let’s start with the basics, shall we?


What is an aquarium sponge filter?

As the name implies – is a porous material that acts as a purification or filtration tool with the main purpose of cleaning the water in an aquarium. If you’re wondering why your fish tank is cloudy, is because you’re not using a filter.

It works by drawing water towards and through the sponge – known as mechanical filtration – and as this action takes place, large debris is prevented from entering the mechanism while small particles may pass through.

The small particles are also debris, however, they are mostly good bacteria which are employed within the aquarium to get and also to keep the aquarium water cycled.

Since sponges are naturally porous, it is therefore not uncommon for such filters to hold a substantial amount of good bacteria.

Good bacteria – also referred to as aerobic bacteria – lives within the pores material and feeds primarily on nitrites waste as well as nitrogenous waste such as ammonia suspended in the water.

This is what happens when the sponge has matured considerably, and bacteria colonies have developed, thus providing biological filtration as well.

They come in a variety of sizes and shapes which determine how they can be adapted to different filtration needs.

They can be powered by several different mechanisms, such as powerheads, air pumps, and even by mounting them to other types of filters.

Sponge filters can be mounted inside the aquarium and under the substrate, too.


How does a sponge filter work?

The process is quite simple. Water is usually pulled through the filtration mechanism via an air pump or a powerhead (which is a submerged water pump that pulls water through the sponge).

When the air pump is turned on, water is drawn – by lift – into the filter, thus causing air bubbles to float up from the pump.

These floating bubbles, in turn, lift the water up and out of the lift tube that is attached to the filter.


What does it filter out?

The sponge acts as a mechanical filter by removing or filtering out solid debris like fish waste, uneaten food as well as other tiny particles in the water.

Therefore, the smaller the pores on the sponge, the smaller the particles it will capture.

This will result in a slow movement as a result of the reduced water flow. To be more precise, it acts as a mechanical filtration unit.

But that is not all it does; an aquarium sponge filter can also act as a biological filtration mechanism.

Biological filtration is a process that is highly crucial in maintaining a healthy environment for your freshwater or saltwater environments.

This is because fish waste leads to the release of ammonia in the aquarium or fish tank and this can be fatal to both fish and plants even if the compound is present in small quantities.

Biological filters, therefore, are beneficial since they have ammonia-eating bacteria which help to break down the ammonia into nitrite, another compound that is still harmful to aquatic life.

The same beneficial bacteria proceed to degrade the nitrite, thus converting it into nitrate which is less toxic to aquatic life.

But the thing is, aquarium sponge filters do not engage actively in the chemical filtration processes. In other words, it is both a biological and mechanical filtration mechanism that is employed in a variety of aquarium setups.


Can sponge purifiers be used for slow filtration?

That’s very possible, indeed. They are excellent when slow filtration is required or needed which is the case in a tank where young fish could accidentally be sucked into the aperture of standard filters.

Some fish species – such as the Siamese fighting fish or betta fish – which do not grow well in strong currents can benefit significantly from sponge filters.

Shrimps also require gentle filtration instead of a strong intake which could suck them in as well.

They are also excellent options for hospital tanks where fish are mostly weak and may not be able to withstand the stronger suction from standard filter inlets.


Pre-filter use

The aquarium sponge filter can occasionally be used as a pre-filter on the narrow opening or inlet of a canister filter.

This method also involves the drawing in of water into the sponge through the HOB(hang on back) filter.

When utilized as a pre-filter, the sponge catches a greater quantity of larger particles which keeps the canister from blockage.

It is, therefore, more manageable – and mostly preferable – to replace or clean the pre-filter frequently.

Moreover, biological filtration is also provided this way as the sponge is ready for use in putting up an alternative or backup aquarium should the need arise.

When using sponge filters with a powerhead, an air pump, canister or another filter, you need to remember that you can add to the setup more than one sponge.

This provides additional mechanical and biological filtering capacity along with the added advantage of allowing maintenance to be alternated so that all the sponges will not be turned off at the same time.



Fish tank sponge filters are somewhat easy to maintain. The key is always to remember to carry out the maintenance process on a regular basis.

Thankfully, it is very easy to see when sponges become dirty. Additionally, the amount of fish, food, plants as well as other factors present in the aquarium can influence how often the filter needs to be kept in good condition.

The best way to clean out a sponge – as recommended by experts – is to carry out a water change which involves saving some of the water that was just removed.

Plunge it in the used aquarium water, and then perform squeeze-and-release actions that dislodge the dirt that has been collected over time.

If this procedure is performed every few weeks, the sponge will never clog totally and will last for a very long time.

These – in most cases – can be used in multiples either by stacking one sponge on top of another or with two inlets.

If, therefore, you’re using more than one for your fish tank, alternate the cleaning schedule so that all the sponges are not done all together.

This will, in turn, reduce the effect on the biological colonies, thus minimizing the potential for nitrite or ammonia spikes after cleaning.


Use cases

Here are a couple of use cases of sponge filters, as part of a more complex aquarium filtration system. This should turn on your imagination.

Using the filter with a powerhead would be best in a scenario that includes:

  • Marine reef appliance
  • Higher flow
  • Less water tension breaking that results in the release of CO2
  • For large fish

If used together with an air pump, on the other hand, then it would be best for the following:

  • Fry tank or breeder
  • Beginners that require simplicity
  • Hospital aquariums
  • For fish that are not rugged enough to tolerate forceful intake such as betta, Discus, etc.

It is therefore very crucial to know the recommended flow rates based on the type of aquarium that is kept.

This will go a long way in determining the kind of flow that will be required: a little flow from air pumps or something more forceful that can only be supplied by a power head.


Pros and Cons of Sponge Filters

Here are some advantages and disadvantages of using such types of sterilizers:


  • Excellent ventilation
  • Inexpensive and easy to use
  • Gentle water flow
  • Safe for shrimp and small fish fry
  • Surface agitation and aeration


  • Filtration capacity is limited for large aquariums
  • Use of air pumps makes sponge filters loud and inefficient
  • Poor aesthetics or visual appeal as they tend to stick out – hard to hide them behind plants or decorations
  • No chemical filtration


Wrapping up

Aquarium sponge filters may not be able to carry out chemical filtration processes but they remain excellent choices in a variety of situations.

We hope that this article shed more light on what an aquarium sponge filter is, what it does and how it can be used to ensure your aquarium remains as clear and clean as possible.

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