Sponge Filters: The Easiest Fish Tank Filter Ever

Because sponge filters are so reliable and simple to use, they are a popular filter in fish shops, fish rooms, breeding tanks, and fish houses. But beginners often have many questions on how they work, how to set one up, and how to keep them clean. Check out our step-by-step instructions to help you get started with your first sponge filter.

Diagram of sponge filter configuration

What is a Sponge Filter and how do they work?

This filter is the most basic. It requires at minimum three components: a sponge filtre (which sits within the tank), an air pump (which sits out of the tank), and airline tubing that connects them. Air is pushed through the tubing by the air pump into the sponge filter’s hollow cavity. The sponge walls draw water through bubbles that rise from the sponge’s interior. This water suction process mechanically collects debris from the aquarium and gives beneficial bacteria place to grow.

Both novice and experienced fish keepers love sponge filters. They are inexpensive, simple to clean, and easy to break. The constant bubbling provides water circulation, surface agitation and good water circulation. It is gentle enough not to eat fish fry, shrimps, or other slow-moving animals. Plus, during power outages, the beneficial bacteria on the sponge stays in the oxygenated tank water (which gives it a longer chance of surviving), and you can even purchase a battery pack backup that works with our USB air pump in case of emergencies.

For more information on filtration options, read our article on fish tank filters and which one you should get.

Do I Need an Air Stone for Sponge Filters?

An airstone is a small accessory that weighs down the airflow from your pump to create smaller bubbles in the water. We recommend adding an air stone to the inside of the sponge filter to lessen the bubbling noise and make the filtration more efficient. The air stone produces a steady stream (instead large, intermittent bubbles), that creates constant lift in the sponge filter. It is similar to an escalator that runs continuously (versus an elevator that stops and starts all the time).

How to Set up a Sponge filter

1. Remove the sponge filter from the foam and the plastic strainer.

1. The bullseye should be removed from the strainer’s top. Place the air stone on the bottom of strainer. Use a short length of airline tubing to connect the airstone to the bullseye’s center or nipple. If the sponge filter is very small, you can simply connect the air stone directly to the bullseye. 2. Snap the bullseye onto the top of the strainer, put the strainer back inside the foam, and then connect the strainer to the weighted base of the sponge filter. 3. Slip the lift tube over one end of the airline tubing roll and connect the airline tubing to the nipple on the top of the bullseye. Then snap the lift tube onto the bullseye. 4. Place the sponge filter into the aquarium and squeeze out any bubbles from the foam if it’s floating. 5. The air pump should be placed in the tank’s final position. Next, cut the airline tubing (attached with the sponge filter) to the right length. Connect the newly cut air tubing from the sponge filter to the air pump. 6. If the air pump is located below the top of the aquarium, you need to add a check valve to prevent water from flowing into the airline tubing whenever the air pump is turned off or the power is out. Cut the airline tubing (between the sponge filter and air pump) a few inches outside of the aquarium, and then attach the check valve in between so that the end of the check valve with the flapper (looks like a colored or horizontal bar usually) is facing the air pump. If you place it backwards, it will not flow air when you turn on your air pump. Instead, flip it over.

1. Create a drip loop with the power cable of the air pump (to ensure moisture will not make contact with the plug), and then plug in the air pump. In a matter of seconds, bubbles should start to form from the sponge filter.

Why are bubbles coming out of the Sponge’s side?

There are several reasons why this could be happening, so try checking the following:

– Did you shorten or remove the lift tube? Because a shorter lift tube doesn’t have as much suction pulling bubbles upwards the center column, some air can escape. Is the sponge filter clogged with air stones? To make it hang straighter, you may need to shorten the tubing attaching the air stone to the bullseye. Is the pump pushing too hard? If a bunch of air is forced into the sponge filter, excess bubbles may leak out the sides.

What sponge filter do you recommend?

Sponge filters are a pretty basic piece of equipment, so there’s not a lot of difference between brands. However, after a decade of using tons of sponge filters, we made our own with all the improvements and features that we’ve always wanted. We made the lift tube and base in a green color so that it blends in with plants and can hide green algae growth. However, the foam sponge is dark to conceal fish waste and other detritus.

The sponge is made of a coarse foam at 20 ppi with medium porosity. It can easily collect particulate and prevents it from clogging up. The sponge’s surface is large enough for shrimp and fish to enjoy. Because the sponge is coarse, it doesn’t trap air as much, so it can sink and get water flow immediately. (Fine sponges often have problems with floating, which can cause lack of oxygen in your aquarium and potentially loss of life.)

All of the sponge filters we sell are hollow inside and tall enough so that you can install an air stone inside for more efficient filtration and quieter bubbles. Also, if you remove the lift tube, you can connect another sponge filter on top (without its base) to increase filtration capacity. The sponges can be made in multiple configurations. Three of the sponge sizes, except the nano sponge, can be mixed and matched together. Stacking multiple sponges, rather than running them separately, has the advantage that they can be run off one air pump line. If you need to set up an emergency hospital tank, just remove one sponge from the stack. It’s already seeded in beneficial bacteria, which will help quarantined fish.

How to Clean a Sponge Filter

Yes, a sponge filter helps to clean your aquarium, but it’s essentially like a trash can that collects waste and needs to be emptied out every once in a while. Your sponge filter should be cleaned once a month. If bubbles are starting to fall, it is likely that the foam has become clogged with debris.

1. When taking the sponge filter apart, disconnect the bullseye from the strainer (i.e., take off the whole top part of the filter) so you can easily remove the foam part for cleaning. 2. Use a plastic bag to scoop the foam out of the water so that the detritus won’t spread and make a big mess in the aquarium. 3. In an old tank of water, squeeze and wring the foam out several times. 4. Reassemble the sponge filter and put it back in the tank. 5. If there are lots of particles floating in the water, just wait an hour or so for the sponge filter to clean it up.

Sponge filters are easy to use, budget-friendly, and very reliable compared to other filter types. Check out our selection of sponge filters to see if you’ve tried one. Let us know your thoughts!