Today’s aquarium fishkeeping hobby has leapt to new heights in terms of tank size and filtration systems. Nowadays it is quite common to see tanks big enough for fishkeepers to actually swim in their own aquariums.

To effectively filter these gigantic tanks, huge sump filters (the size of the aquariums about which we used to proudly brag to our friends) are made. Big, technically advanced, and simply mind-blowing tanks are now realities in the Philippine aquarium scene.

It is a real fact too that for modest or average Filipino fishkeepers, the tanks mentioned above are merely a dream. Those tanks are simply too much and they will never own one. For these fishkeepers, a 20-gallon tank is a reality, and dreams are realized with it. 20-gallon tanks can be so much fun. Well, we in the hobby all know that since we all had our 20-gallon tanks, right?

For a regular Filipino fishkeeper, a 20-gallon tank will most probably be filtered by either a sponge filter or an overhead filter (OHF). These are the two most common options for a tank of this size. I am often asked which is better, to which my reply is always a smile. There is no one correct answer. Let me share my discussion points in this article.

Before we start, let me put everyone on the same page by describing the setup of two 20-gallon tanks. Setup One is a bare 20-gallon tank with 4 wild-form Angelfish with a sponge filter. Setup Two is a bare 20-gallon tank with 4 Marble Angelfish and an OHF. Both tanks are identical, with the filters being the only variable.

How They Work

To start the discussion, let us begin with the technology behind the two filter systems. The sponge filter consists of foam—which acts as the biological filter media where beneficial bacteria will thrive; a lift-up tube at the center of the filter material; an air hose; and an air pump that runs the filter. Air is driven into the air pump through the air hose, which is connected to the sponge filter.

As the air passes through the lift-up tube, air bubbles are created and these float to the surface. This causes a pulling action, and water from the tank is displaced through the foam and the lift-up tube; at the end, filtered water is returned to the tank.

In Setup One, the sponge filter will prove to be an efficient biological filter as it will be able to support a healthy colony of beneficial bacteria that will be able to process the bioload from the 4 wild-form Angelfish. In our second setup, a Sea Quest 600 powerhead pumps water from the 20-gallon tank up to the overhead filter box, which measures 13 inches (in) by 5 in by 3 in. Water is filtered through a layer of ceramic rings and filter wool. The filtered water then flows back to the main tank, pulled by gravity through the return overflow.

The OHF should be able to develop a rich, healthy colony of beneficial bacteria to easily process the bioload created by the 4 Marble Angelfish. This setup should be able to provide crystal-clear water.


From a technological standpoint, let us compare the two setups in terms of capacity and flow rate to determine efficiency of the two filter systems. The capacity of the filter system is the volume of filter material that becomes the home of your beneficial bacteria. The bigger the volume of filter materials, the bigger your beneficial bacteria colony will be. Thus the more filter media you have, the bigger the capacity of your filter to process aquarium water in your system.

In our first setup, I measured the foam filter, and the dimensions revealed a diameter of 4.5 in with a height of 4 in. Using the formula for volume of a cylinder, the sponge filter I used had a volume of 63.62 cubic in of filter materials. On the other hand, the filter box of the OHF I used measures 13 in by 5 in by 3 in, resulting in a volume of 195 cubic in of filter materials. This is 3 times more than that of the filter material volume of the sponge filter.

Therefore, in this instance, the OHF has a bigger capacity: 3 times more than the sponge filter. This does not even consider the type of filter material used. Beneficial bacteria thrive on the surface of the material. More than the volume of filter media, what is critical is the total surface area in that given volume of media. The ceramic ring was developed specifically for fishkeeping because it has far more surface area than a foam filter given the same volume.

The second aspect to consider is flow rate. Flow rate is the volume of displacement of water through the filter media over time. The sponge filter is run by an air pump. When air passes through the lift-up tube, the air forms bubbles that naturally float to the surface. This process incidentally displaces water in the tubes in between bubbles. As the bubbles move up, water is gently displaced.

Unfortunately, I have no means to measure this, and it is beyond my mathematical competency to compute for this. But if I were to describe the flow rate in fishkeeper’s terms, then I would describe it as a weak flow rate. The OHF, on the other hand, is equipped with a powerhead rated at 600 liters per hour. This converts to 158 gallons per hour. This means that there is a turnover ratio of about 8 times in an hour. Water in the 20-gallon tank is run through the filter box and processed 8 times per hour.

That is 192 times a day or a displacement of 3,840 gallons in a 24-hour cycle. That is an amazing ratio that can guarantee crystal-clear water. From a technical perspective, the head to head comparison of the two proves that the OHF clearly is a far more efficient filter system in terms of capacity and flow rate over the sponge filter. It has three times better capacity and an impressive flow rate.

The Overlooked Human Factor

But before you OHF users start cheering and celebrating, this of course is merely a comparison in terms of the technology behind the system. Always remember that behind every successful (or unsuccessful) tank is a fishkeeper. This is where human intervention can make a difference. A sponge filter is a great biological filter. The whole sponge is one biological filter.

It has no mechanical filter capability which is responsible for removing solid waste matter. Only the smallest debris is trapped within the crevices of the sponge. The biggest ones end up on the tank bottom, gathering into unsightly piles. This is the biggest weakness of the sponge filter: poor or almost zero mechanical filtration capability. This is creates an eyesore, so the fishkeeper is forced to do a partial water change every 3 or 4 days.

This is definitely hard work that is forced upon fishkeepers. But without them knowing it, they are actually making things so much better for their fish. Their objectives may be to clear the tank of solid waste, but as a result of the frequent water changes, they are actually clearing their tanks of toxic substances like ammonia, nitrites, and nitrates.

They may have a weak but adequate filter in the sponge filter, but their participation in the form of frequent water changes ensures that their water is of optimum quality. Without meaning to do so, they have improved the water quality in their tanks. This is a great side benefit. On the other hand, the OHF picks up solid matter efficiently as these are trapped by the filter wool, leaving the tank nice and clean. But since fishkeepers see a clean tank, they can forget to do weekly partial water changes. With all the fish waste efficiently gathered in the filter box and effectively processed, in time, nitrate levels may gradually increase.

If fishkeepers are not dedicated to periodic water changes, then there is a great danger of nitrates increasing to toxic levels without them ever noticing because their tanks are clear. Let’s face it: fishkeepers may be reactive in their actions. If they see that their tanks are clear, then they may opt not to do any water change. But if they see dirt at the bottom of the tank, even if they feel lazy, they will (usually) take the time to siphon the dirt off.


So now we go back to the same question. Which filter is better: a sponge filter or an OHF? This is why I always answer with a smile. From a technological viewpoint, hands down, my choice is an OHF. But to get the totality of keeping water in optimum quality, it is a toss-up. Both are actually good filters but how we intervene as fishkeepers can make a big difference.

In trying to achieve good water quality, keep in mind that filtration is only one component of the equation. Filtration is the technology that enables the breakdown of toxic substances in the aquarium water to less toxic substances. However, your periodic maintenance schedule keeps the water quality in optimum conditions. So even if you have a high-tech, very expensive, top-of-the-line filter system, you should still be religious with your frequent water changes.

Therefore, to achieve top water quality, filtration and maintenance should go hand in hand. You must have a good filter and an efficient maintenance system to make sure your water is good enough for your fish to live. One without the other will never work, and will never give you the desired results you are trying to achieve.


This appeared as “OHF Vs. Sponge Filer: Which is Better?” in Animal Scene’s May 2016 issue.