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. Many people are unsure how sponge filters work and how to clean them. 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?

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. Bubbles rise from the inside of the sponge, thus drawing water through the sponge walls. 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. Because of the constant bubbling, it provides good water circulation and surface agitation, white being gentle enough to avoid sucking up fish fry, shrimp, and other slow-moving creatures. You can also purchase a backup battery pack that will work with our USB pump to keep your sponge alive during power outages.

You can find more information about filtration options in our article Fish tank filters. Which one should you get?

Do I Need an Air Stone for Sponge Filters?

An air stone is small, lightweight accessory that helps to diffuse the air from the pump and create smaller bubbles in 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. Take apart the sponge filter and remove the plastic strainer from the inside of the foam.

1. Remove the bullseye from the top of the strainer, and put the air stone at the bottom of the 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. Place the bullseye on the top of the strainer and then attach the strainer to its weighted base. 3. The lift tube should be placed over the end of the roll of airline tubing. Connect the cable to the nipple at the top of your 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. Place the air pump in its final location outside of the tank, and then cut the airline tubing roll (attached to the sponge filter) to the proper length so that it’s long enough to reach the air pump. The sponge filter’s air tubing has been connected to the 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. It is best to flip the check valve around so that air doesn’t flow if it is installed backwards.

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. After a few seconds you will see bubbles 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? You may have to reduce the length of the tubing connecting the air stone to your bullseye to make it hang straighter. Is the pump pushing too hard? Excessive bubbles can leak from the sides of the sponge filter if too much air is forced into it.

What sponge filter do you recommend?

Sponge filter are a very basic piece, so there isn’t much to choose from. After using hundreds of sponge filters for a decade, we decided to make our own. 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 from a coarse foam with 20 ppi and medium porosity. This allows for particulate to be collected easily without clogging too quickly. It is easy for fish and shrimp to use and easy to clean. Plus, the coarse sponge doesn’t trap as much air, allowing it to get nice water flow and sink 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. These sponges can be customized in multiple configurations, since three of the sponge sizes (all except for the nano sponge) can be mix and matched together. A stacking of sponges is more efficient than running them individually. They can all run on a single line of air pump. Then, if you ever need to set up a hospital tank, simply remove one sponge from the stack and it’s already seeded with beneficial bacteria to help the 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. You should clean your sponge filter at least once per month. Also, if you notice a decrease of bubbles (which can be caused by foam becoming clogged with detritus), we recommend that you empty it out.

1. To clean the sponge filter, remove the bullseye and strainer from it. 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. Now, assemble the sponge filter and place it back in your tank. 5. You can wait for the sponge filter to remove any large particles that are floating in the water.

Sponge filters can be very cost-effective and reliable, making them a great choice for budget-minded users. Check out our selection of sponge filters to see if you’ve tried one. Let us know your thoughts!