How to Improve Water Circulation on Aquarium Sponge Filters

Sponge filters are one of the most popular types of aquarium filtration, frequently used by fishkeeping veterans, wholesalers, and fish farms who breed millions of ornamental fish. Not only are they simple to use and easy to clean, but they are extremely reliable since they have very few mechanical parts. Plus, sponge filters are gentle enough that they won’t suck up any baby fry, dwarf shrimp, or betta fish with long, flowy fins. However, sometimes the flow can be a little too gentle and not produce enough water circulation in the aquarium. How can we solve this problem?

Normally, a sponge filter works like this:

1. An air pump is placed outside the aquarium, and it pushes air through the airline tubing that is connected to the hollow center inside of the sponge filter.
2. As the bubbles rise inside the sponge filter, water rushes in through the sponge material, trapping particles in the sponge walls. (These particles serve to feed the beneficial bacteria that help purify the aquarium water of harmful chemicals produced by your fish’s waste.)
3. The bubbles in the middle of the sponge flow out of the uplift tube and pop at the surface, creating surface agitation.

For the Aquarium Co-Op sponge filters, we designed a curved uplift tube called “Easy Flow” to redirect the current so that it shoots bubbles and water horizontally across the surface. This simple change has several significant benefits that have improved the overall filtration performance in our aquariums.

Aquarium Co-Op sponge filters in four different sizes

1. Better Circulation

People don’t talk about water circulation in the freshwater aquarium hobby as much as they do in the saltwater hobby, but it affects the health of the ecosystem in so many ways. Good water current helps to evenly distribute oxygen, plant fertilizer, baby brine shrimp, powdered foods for baby fry and filter feeders, and more in the aquarium. When you have a fish tank (especially a bigger one) that is crammed with rocks, driftwood, and decorations, it can develop dead zones where it’s hard for the water flow to reach. These stagnant areas often build up piles of unsightly debris and algae growth. By aiming the spout of the Easy Flow toward these sluggish spaces, the detritus is stirred back into the water column, allowing it to be sucked up by the sponge filter.

For example, most people place the sponge filter in one of the back corners so that it is out of sight. If you have a bunch of plants or other decor blocking the way, then the current is much slower in the front of the tank and mulm (i.e., the fluffy, brown “dust” on the substrate) tends to collect there where it’s the most visible. Instead, aim the Easy Flow uplift tube so that the spout aims toward the middle of the front aquarium wall. The current will flow across the surface, hit the front wall, and travel downwards, thus pushing the mulm towards the middle and back of the aquarium so that it’s less obvious.

Aiming the Easy Flow towards the front wall pushes back the mulm and makes it easier for the sponge filter to pick up the debris.

2. Better Surface Agitation

Moving water at the top of the aquarium is vital to your fish’s health because it encourages good gas exchange, in which carbon dioxide (a waste product produced by your fish) exits into the air and new oxygen from the air dissolves into the water. In a past experiment, we showed how filters that agitate the water surface have much higher levels of dissolved oxygen levels in the tank.  With a traditional sponge filter that has a vertical uplift tube, the bubbles rise and creates circular ripples in the area just above the sponge filter.

However, the spout of the Easy Flow uplift tube can be easily extended to sit right at the water line so that the bubbles and water flow shoot horizontally across the tank, boosting the amount of surface agitation. Not only does this prevent an oily biofilm from developing on the water surface, but it can also push away floating plants, creating a larger area for gas exchange to occur. If you find that the current at the surface is too strong for some of your top-dwelling fish, the Aquarium Co-Op air pump has an adjustable air flow control or you can install an air valve to lessen the speed.

The Easy Flow uplift tube extends to sit right at the water line to produce optimized, horizontal flow.

3. Improved Bubbling

One complaint that fishkeepers sometimes have about sponge filters is the bubbling sound when the bubbles pop at the surface. Some people find the sound calming, while others don’t want their tank to sound like a witch’s cauldron. Our founder Cory runs an entire fish room with more than 30 tanks, most of which have sponge filters. The compounding effect of that many sponge filters definitely raises the general noise level of the fish room. Since switching over to the Easy Flow uplift tubes, the measured decibel level of the fish room has significantly dropped to approximately 40 dB, which is comparable to the noise level of a quiet library. Rather than greatly agitating the water in a single, concentrated location, Easy Flow helps to evenly distribute the bubbles (and their popping noise) across the entire tank’s surface, minimizing the overall sound.

Besides the decibel level, we’ve also observed another benefit caused by the different bubble popping pattern. In a traditional sponge filter, the bubbles all pop in roughly the same area of the tank, causing water to splash up and stick to the aquarium lid and rim. This excess moisture often causes dark green algae sludge to grow, as well as white mineral deposits to form if you have harder water. In contrast, the horizontal surface current of the Easy Flow causes the bubbles to travel further and not always pop in the same spot, thus reducing the amount of moisture on the lid and rim. Take the previous case where the sponge filter is in the back corner and the Easy Flow uplift tube is aimed towards the middle of the front wall. Depending on the air pressure of the air pump, most of the bubbles end up popping somewhere in the middle of the tank, leaving the rims free of crusty mineral deposits. Plus, the glass lid is somewhat dryer than before, reducing the growth rate of the algae sludge.

If you have a glass lid and are using an external aquarium light like the Easy Plant LED, then we have a bonus trick to prevent algae growth on top of the Easy Flow uplift tube itself. Purchase a plastic, black folder, and cut out a square or rectangular piece that is large enough to shade the top of the Easy Flow. Place the plastic folder piece on the glass lid so that it is under the light and covers the Easy Flow. Generally speaking, you will not have plants growing directly where the sponge filter is, so a little bit of shade in that corner of the tank won’t negatively impact the plant growth.

Shade out the corner where the sponge filter sits to prevent algae growth on the Easy Flow.

4. Efficient Flow

Normally, a sponge filter creates large, intermittent bubbles that have a loud, glugging sound. However, if you can make the bubbles much smaller, it reduces the noise level and makes the filtration more efficient. A steady stream of tiny bubbles produces continuous lift and suction in the sponge filter — similar to how an escalator runs continuously whereas an elevator starts and stops a lot.

In order to create this flow of little bubbles, we previously recommended the use of an air stone inside of the sponge filter. Over time though, the airline tubing that connects the air stone to the sponge filter would eventually harden, causing the air stone to slip or completely drop off. Therefore, we designed the Easy Flow uplift tube to come with an air collar at the base, which also diffuses the air from your air pump into smaller bubbles in the water. The air collar completely replaces the air stone while still having the same benefits of quieter bubbling and optimized filtration. Plus, it completely prevents any pesky bubbles from escaping out the side of the sponge walls.

Air collar produces smaller bubbles for optimized filtration

If you have never used a sponge filter with an adjustable, curved uplift tube, you need to try the Aquarium Co-Op sponge filter. For the older versions of our sponge filter, you can buy the Easy Flow upgrade kit for the small, medium, and large sizes, as well as for nano sizes sold in 2024 or afterwards. If you purchase any of our sponge filters nowadays, they all include the handy-dandy Easy Flow uplift tube, so give it a shot and instantly improve your aquarium filtration.