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. For step-by–step instructions on how to make your first sponge filter, see our guide.

Diagram for sponge filter setup

What is a Sponge Filter?

This most basic of all filters requires at least three components: a sponge filter (which sits inside the tank), air pump (which sits outside the tank), and airline tubing to connect them. The sponge filter is hollowed by air pumps. 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. In case of emergency, you can purchase a battery pack backup to work with our USB air pump.

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 air stone is a small weighted accessory that diffuses the air from your air pump into 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 airstone creates small bubbles that are steady and continuous, rather than intermittent large bubbles that move in a slow fashion. This gives the sponge filter constant lift.

How to set up a sponge filter

1. You can remove the sponge filter by removing the plastic strainer.

1. Remove the bullseye from the top of the strainer, and put the air stone at the bottom of the strainer. Connect the air stone to the nipple or center of the bullseye using a small length of airline tubing. The sponge filter can be connected directly to your bullseye, if necessary. 2. Place the bullseye on the top of the strainer and then attach the strainer to its weighted base. 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. Place the air compressor in its final place outside the tank. Then, cut the airline tube roll (attached at the sponge filter), to the correct length. 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. If you place it backwards, it will not flow air when you turn on your air pump. Instead, flip it over.

1. Make a drip-loop with the power cable to the air pump. This will prevent moisture from coming in contact with the plug. Finally, plug the air pump into the outlet. After a few seconds you will see bubbles from the sponge filter.

Why Do Bubbles Come Out of the Sponge Side?

There could be many reasons this might happen. Check out the following:

– Did you reduce or remove the lift tub? A shorter lift tube does not have as much suction pulling bubbles up the center column, so some air may escape. – Is the air stone crooked inside the sponge filter? The tubing that connects the airstone to the bullseye may need to be shortened to allow it to hang straighter. Is the pump pushing too hard? If a bunch of air is forced into the sponge filter, excess bubbles may leak out the sides.

Which sponge filter would 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. The base and lift tube were designed with a green color to blend with the planted tanks and hide green algae growth. The foam sponge is black to conceal any fish waste or other debris that might get sucked in.

The sponge is made with a coarse foam of 20 ppi medium porosity to easily collect particulate from the water without clogging up 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.)

The sponge filters that we sell are hollow in the middle and high enough to allow you to install an airstone inside. This will increase efficiency and create quieter bubbles. You can also connect another sponge filter to the top of the lift tube (without its base), to increase your filtration capability. The sponges can be made in multiple configurations. Three of the sponge sizes, except the nano sponge, can be mixed 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. 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!