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What is a sponge filter and how does it work?

Jun. 12, 2020

A sponge filter is little more than a piece of foam that sits inside your aquarium and filters your water.

No, seriously – it’s as simple as that!

While sponge filter designs vary from brand to brand, they are typically made up of four different parts:

sponge filter

Different parts of a sponge filter diagram

1. Foam sponge – It wouldn’t be a sponge filter without it.

2. Weighted base – Stops the sponge filter from floating around your tank. The sponge sits on top of this base.

3. Strainer and bulls eye–Slides inside the sponge and allows you to connect airline tubing directly to the filter.

4. Lift tube – Water flows up this and back into your tank.

While it may not look like much, these four parts actually form a very effective filter.

As for how a sponge filter works, well, it’s very clever…

sponge filter

How a sponge filter works diagram

With a good air pump attached, bubbles rise up the lift tube and out into your tank.

This forces water to be drawn through the foam sponge.

As water passes through the sponge, it catches and traps debris, such as fish poop, uneaten food and decaying plants, filtering it from the water.

Filtered water then passes through the lift tube and back into your tank.

While this filtration method may seem basic, it’s quite effective!

Since sponge filters don’t have a way to force water through them, they are used in conjunction with an air pump, airstone or powerhead. Without one, they are useless.

If you have never heard of a sponge filter before, it may surprise you to learn that they have been around a long time.

While they used to be the preferred way to filter an aquarium, advancements in filter technology have seen the sponge filter become less popular.

But sponge filters are still incredibly useful for your tank!

While sponges continue to make a great cheap primary filter, they are also often used to add an extra layer of protection to your tank.

When used this way, sponge filters are sometimes referred to as pre-filter sponges because they are exactly that – a sponge that sits on your filter tube intake.

Water passes through the sponge before it reaches your filtration system.

Yep, you can use a sponge filter in addition to your primary filter, such as a canister filter, to preventing it from clogging.

Depending on your setup, a sponge filter could be the perfect addition to your aquarium.