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How to Customize Your Aquarium Filter with Filter Media

Aquariums can widely differ in their size and stocking levels, so it makes sense that people want the ability to customize the filtration to best suit their needs. Most filters – such as hang-on-back (HOB), corner box, internal, canister, and sump filters – can be modified by changing the types of filter media used inside. Filter media refers to the different layers of materials that tank water gets filtered through before returning to the aquarium. Keep reading to learn about the different kinds of media, the functions they serve, and which ones you should use.

1. Mechanical Filter Media

Mechanical filtration consists of sponges, foam pads, and filter floss that physically strain out debris from the water, much like a coffee filter. Mechanical media is porous so that water can still flow through it, and the size of the pores determines what size particles are caught in the material. Coarse sponge pads with large pores are good for blocking most debris like fish poop and dead leaves, and when they become full of waste, you can squeeze them out in old tank water and reuse them over and over again. Also, they don’t clog up as quickly, so you don’t have to constantly clean them. We often use sponge pads to replace the disposable filter cartridges that come with many aquarium kit filters.

If you’re still seeing tiny particles floating in the aquarium and want to get crystal clear water, try adding a fine poly pad or filter floss. This mechanical filter media has very fine porosity that can catch the tiniest bits of flotsam and jetsam in your aquarium. Because the floss pads are very dense by design, they can clog up easily and should be replaced when they turn brown in color. Both the coarse sponge pad and fine poly pad can be customized by cutting them into smaller sizes so that they fit your filter perfectly.

aquarium mechanical filter media

Fine poly pad (left) and coarse sponge pad (right) for mechanical filtration

2. Biological Filter Media

Biological filtration refers to the usage of beneficial bacteria and aquarium plants to consume the toxic nitrogen chemicals generated from fish waste, thus purifying the water. Because beneficial bacteria grows on any surface area in the tank that is well-oxygenated, the filter is a primary location to boost the population. Biological media (such as bio rings and bio balls) come with lots of porous or intricately patterned surfaces to serve as “housing” for the bacteria colony. (In fact, beneficial bacteria also readily grows on the coarse sponge pads used for mechanical filtration.) The shape of the bio media also allows water to flow freely though them to bring more oxygen to the bacteria. Aquarium gunk can cover these surfaces over time, so clean the bio media every 1-3 months by gently waving or rinsing it in old tank water until the debris falls off. (If you are using loose bio media that does not come in a bag, put it in a filter media bag to make it easier to pick up and clean.)

aquarium bio rings - filter media

Aquarium bio rings for biological filtration

3. Chemical Filter Media

Chemical filtration has the ability to remove pollutants and certain chemicals from the water. The most common type is activated carbon, which is a highly porous charcoal that readily absorbs medications, tannins, and other impurities. Activated carbon for aquariums usually comes in loose granules and must be contained in a filter media bag. We prefer using carbon-infused media pads because they are easier to handle, can be cut down to a custom size, and provide increased mechanical filtration for straining debris from the water. You can even cut out a section of the pad to wrap around a sponge filter with a rubber band or zip tie for added chemical filtration. Once the charcoal pores are filled with pollutants, the activated carbon media is no longer functional and must be replaced.

If you prefer to have reusable chemical filtration, get a synthetic adsorbent like Purigen instead. The polymer granules come pre-packaged in a media bag, ready to absorb organic waste and tannins. Once the adsorbent changes color from off-white to dark brown, the pores in the polymers have become saturated and must be cleaned. Follow the manufacturer’s instructions to create a diluted bleach solution that burns off the organic impurities so that the Purigen bag can be reused again.

Some kinds of filter media are designed to target and filter out specific chemicals. For example, ammonia spikes are prone to occurring when the balance of your fish tank has been disrupted, such as after moving an aquarium, experiencing a power outage, or thoroughly cleaning a fish tank. To prevent toxic levels of ammonia from building up, you can preventatively install an ammonia filter pad to absorb the ammonia and keep your fish safe.

If phosphate levels are excessively high in your aquarium, it can lead to algae growth and compromise your fish’s health. Try using a phosphate media pad to keep the phosphate under control so that algae can’t take advantage of it. When keeping live aquarium plants, some planted tank articles recommend keeping approximately 0.5-2.0 ppm phosphate for healthy plant growth, so don’t remove too much phosphate or else you may see yellowing and browning in the leaves.

chemical filtration pads

Carbon-infused, ammonia, and phosphate pads for chemical filtration

Frequent Asked Questions about Filter Media

What order should I put the aquarium filter media? There are many ways to layer the filter media in your filter, so these are our general suggestions. The first step is to look in the manual and find out which direction the water flows through the filter. As the water enters the filter media basket, we like to use a coarse sponge pad as mechanical filtration to block the largest chunks of debris and prevent them from entering the rest of the filter media. If you need to use the ammonia or phosphate media pads, you can place them here since the pads also serve as mechanical filtration. As a final mechanical filtration layer, you have the option of adding the fine poly pad to catch even smaller particles floating in the water.

The next layer is the biological filtration, so fill the media trays with bio media. Finally, you can choose to use chemical filtration like activated carbon or Purigen at the very end right before the water leaves the filter and reenters the aquarium. Not all of these products are necessary, but we do recommend having at least one layer of coarse mechanical filtration and then one layer of biological filtration if you have room.

How do I clean an aquarium filter without killing bacteria? Remove the filter media and rinse them in old aquarium water or dechlorinated water to remove any accumulated waste. Coarse sponge pads are the dirtiest and can be vigorously wrung to clean it as much as possible. Bio media houses beneficial bacteria and should be gently agitated (not scrubbed) in the water. Chemical filtration needs to be replaced entirely when used up (unless you’re using Purigen, which can be cleaned with diluted bleach). The frequency of filter maintenance depends on many things, like the size of the filter, amount of media, and amount of food being fed to the aquarium. As a rule of thumb, we recommend setting a calendar reminder to clean your filter every 1-3 months.

aquarium filter media bag

Place loose media (like activated carbon and bio media) in a filter media bag to make it easier to contain and move around.

How long does aquarium filter media last? Reusable filter media – such as the coarse sponge pad, bio rings, and Purigen – can last for many years, as long as it can be cleaned sufficiently so that its functionality is not impaired. Fine poly pads should be disposed when they turn brown in color and water cannot move through them as easily. The only way to tell if chemical filtration like activated carbon, ammonia media pads, and phosphate pads are spent is to measure the water. If you have tannins or odd odors in the water and the activated carbon no longer gets rid of them, it’s time to replace it. If you are measuring ammonia or excess phosphate in the water, then the chemical media pads are likely saturated and no longer functional.

Do I need carbon in my aquarium filter? Because activated carbon (and most chemical filtration) is disposable and cannot be reused, we like to save it for specific instances when we know there are pollutants or tannins that we wish to remove. If you are preparing for an aquarium photoshoot, you may choose to use carbon to ensure the water is extremely clear. However, most hobbyists do not use carbon on a daily basis because it gets depleted so quickly and the results may be temporary.

To take your fish tank filtration to the next level, learn how to upgrade your aquarium filter with filter media in four easy steps.

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