How Does A Sponge Filter Work? Is One Right for Your Aquarium?

There’s a great kids book called “Everyone Poops”. It very matter-of-factly explains, at a child’s level, that all living creatures defecate. The aim is to make potty-training children understand this is a natural process.

I suppose it’s very helpful for young parents, but if the sub-purpose was to take the humor out of scatology, it failed entirely.

Now to my point: everyone and everything poops, including your exquisite tropical fish. Where does all that excrement go? Right into the water, of course.

A beautiful white betta fish in a planted tankTo keep all that nastiness from fouling up the tank and creating a toxic environment for your fish and other creatures, you need to use a filter. There are many kinds of aquarium filters out there. How to choose?

Today we’re going to explore the world of sponge filters.

We’ll look at how sponge filters work, what they’re good for, and what they’re not good for. In the end, hopefully, you’ll know whether one might be right for your aquarium.

Are you ready to absorb some information?

What Is A Sponge Filter?

They are any style of aquarium filter where the water from the tank is pulled through a sponge and into a lift tube.

How Does a Sponge Filter Work?

The sponge itself is wrapped around a central core, usually a plastic frame of some sort. Attached to the core you’ll find a lift tube and an air hose running from a good aquarium air pump. The lift tube stays submerged, but the air hose exits the tank and connects to an air pump.

Air pumped through the air hose creates bubbles in the core. You’ll see the bubbles rising up the lift tube shortly after you switch on the pump. These tiny bubbles ascending the tube create suction that pulls aquarium water through the sponge.

The sponge does double duty as a filter. What you can see is mechanical filtration, with the filter stopping large particulate from continuing to circulate through the tank.

What you can’t see is the sponge performing its most important job. The many nooks and crannies and large surface area provide a home for colonies of good bacteria.

These bacteria act as biological filtration, happily feeding on ammonia and converting it to nitrite, and then to nitrate. Nitrate is still mildly toxic, but it’s WAY better than the other two. This process is part of the “nitrate cycle”, and it happens in all aquatic biosystems.

Different Types

There are a few different types of sponge filters, though they all work the same way.

Some models rest on the bottom of the tank and can be positioned anywhere that’s convenient. Although not common, there are models that go under the gravel. (If you use sand for substrate, don’t bury the sponge. It will just clog the holes and prevent it from doing its job.)

Smaller models attach to the wall of an aquarium using one or more suction cups. These are widely available in either one or two sponge configurations.

Some external filters use a sponge like media as part of a series of filters for maximum benefit. Tanks like the Biocube series have a spot built into the filtration system for such media too.


Taking care of a sponge filter is easy. You can simply rinse it under lukewarm running water to dislodge the solid matter. Do not use hot or cold water, and don’t run the water too hard. Doing any of those things can be detrimental to your bacteria colony.

The best option is to clean your filter when you do a water change. Collect your water to be discarded in a bucket and gently squeeze the sponge in the old tank water before pouring it away This will remove the solid waste without harming much of the bacteria.

If your aquarium or filter has more than one sponge, do not clean them all at once. Staggering your cleanings is the best way to ensure a healthy bacterial colony is always present.

Is A Sponge Filter Right For My Aquarium?

They provide very gentle filtration for a tank. They are especially effective in tanks where minimal water movement is needed.

If you like to breed fish, they are a perfect choice for your fry tank. In fact, they are sometimes referred to as ‘breeder filters’.

The low-level suction is well suited to tiny fins, and there is no chance of losing fish into the filtration system. You’ll probably find the young fish enjoy nibbling on the microorganisms growing on the sponge, too.

For all these same reasons, any tank with small fish, frogs, or shrimp is well suited to a sponge filter. Fish with delicate fins, such as bettas, or who are poor swimmers will also appreciate the safety of such a gentle filter.

They’re also great for quarantine or hospital tanks, or any tank that is essentially devoid of décor. Tanks without decorations cannot develop biological filters of their own because there’s nowhere for the bacteria to live. Sponge filters also won’t filter out medications, unless they have an activated charcoal component.

For a very large aquarium or one with strong currents, one on its own may not provide enough filtration. Including one as a secondary filter is never a bad idea, however. You can even take one with a healthy colony out of a big tank with other filtration, and use it to help establish a new tank.

If you’re very concerned about aesthetics in your aquarium, then a sponge filter might not be right for you. Many models are difficult to hide due to the size of them. You wouldn’t want to spoil your carefully cultivated aquascaping with a big nasty filter center piece inside your tank!

If you have a few minutes to spare, here’s a great and informative video that takes a close look at how they work.


Old School Problem, Old School Solution

What do you think? Is a sponge filter right for your aquarium set up? Though there are some who consider this old school and not worth bothering about, we think there’s a place for them in nearly any aquarist’s life. It’s safe, effective, and it’s cheap!

If you’re new to our site, we’re happy you found us today during your search for the best aquarium resource on the web. If you’re a regular, welcome back!

As always, we encourage you to share your discovery with others. Your continued support allows us to keep posting, and keep making your life aquatic more enjoyable.

Happy fish keeping!

Wendy Kathryn

Hi, I'm Wendy, the owner and creator of this website, an experienced fish keeper and avid student of the art since 2010. My aim is to help beginners avoid the many possible mistakes when getting started in this wonderful hobby.

2 thoughts on “How Does A Sponge Filter Work? Is One Right for Your Aquarium?”

  1. More detailed question with pictures and videos coming up. Please clarify this, i. The poop settles down. How do the sponge filters pull it in through? They’re unable to even lift/pull the deliberately disturbed detritus/leaves/roots inside. ii. Are they even supposed to do so?

    • Hi Ra,

      What you say is correct. A spoge filter is one of the weakest types of filter. But really, their job is more for biological filtration: Establishing and maintaining the nitorgen cycle via a colony of friendly bacteria that convert harmful chemicals in the water into less harmful ones.

      Some solids in the water do get collected by the sponge, which will be evident if you inspect the sponge after some time, but yes the majority of detritus will fall into the substrate and stay there.

      But honestly, this happens with every and any filter. Large waste (from fish, uneaten food, etc.) will always fall into the substrate. No filter will be able to suck up this waste, and in fact if they could, it would have to be so poweruful it would be uncomfortably powerful for most fish to be able to live in the tank withough being sucked in too!

      Therefore, regular cleaning of your sand / gravel with a gravel vacuum is a part of routine tank care.

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