Aquarium Fish

Filter Media: Types and Functions

posted: 05/15/12

Filters are essential for the health of your aquarium. They keep the nitrogen cycle going and help keep your tank inhabitants healthy.

Filter media is anything placed in a filter that changes the quality of water flowing through it. With the variety of medias available, specific types can be chosen to create the optimum environment in your aquarium.

The three types of filter media are:

- Mechanical

- Biological

- Chemical

All three types are recommended, but an aquarium needs to have biological and mechanical filters at minimum. Components of these media types can be incorporated in the same filter. The three types of filtration utilize three different types of media to perform their functions. This article will help you weave through the maze of terminology and differences between the media that filters use.

Mechanical media

The components of mechanical media are inert — this means they will do nothing to interfere with your water chemistry. This media mechanically or physically strains solids from water passing through it, which is vital for the efficiency of your biological media. Mechanical filtration removes unsightly particles including fish excrement, sludge, uneaten food, or dust. To prevent build-up, the filter media must be cleaned regularly. Replacement is only required when the media can no longer release all the dirt that it holds.

Mechanical media is available in many different porosities, which limit the size of the particulate they can extract. The larger the pores in the mechanical media, the larger the particulate matter must be in order for the filter to extract it. Coarse media is easier to clean and reuse than finer media. The pores in the finest mechanical media strain out particles as tiny as one micron, which is 1/90 the diameter of a human hair! The finest media will clarify the tank, but will clog very quickly, and may not be reusable.

Filter Media Type: Ehfimech or Fluval prefilter media

Grade Type: Very coarse

Usage: Catches large debris so that small media does not need to be cleaned as often.

Filter Media Type: Ehfifix, Blue Bonded filter pads, foam blocks

Grade Type: Coarse to medium

Usage: Cleans most visible debris.

Filter Media Type: Filter floss and Ehfisynth

Grade Type: Fine

Usage: Filters out fine particles providing crystal clear water.

Filter Media Type: Micron filter pads or filters utilizing diatomaceous earth

Grade Type: Extra fine

Usage: Removes extra small particulate, even parasites and bacteria.

Biological media

Biological media is anything inert that provides housing for beneficial bacteria that break down dissolved solids to a less toxic form. This is a media that should not be replaced unless it has become too clogged to function.

To understand this media, first we must understand what the bacteria used for biological filtration need to thrive:

- Environment above 55°F

- Ammonia or nitrite as food source

- Oxygen

Bacteria extract food and oxygen from the water passing over them. When particulate matter gets into the media, decreasing water flow, it "starves" that area of oxygen and food, causing bacteria in that area to die. This is why mechanical media should be placed before biological media.

When the bio load increases, the abundance of ammonia and nitrite causes the bacteria to reproduce. Bacteria that consume ammonia reproduce quickly, until the ammonia level drops to zero. Sometimes they over-produce and cause a "bacteria bloom" that looks similar to smoke in the aquarium. Once the correct amount of bacteria have grown to overcome the ammonia spike, the excess bacteria starve and die, and the "smoke" disappears. It is easy to see why aquarists insist on a minimum of biological and mechanical media for filtration. They work in harmony and help keep a healthy, balanced, and reliable ecosystem.

In an established tank, a bacteria bloom is less likely to happen and any ammonia spikes may be gone in 24 hours — often before you even have time to test for it. In new tanks, the time the ammonia takes to be converted by bacteria depends on the amount of fish load and bacteria you start with.

As the ammonia-eating bacteria consume ammonia, they give off nitrite. Other bacteria consume the nitrite for energy. These bacteria are slower to reproduce, and prefer environments in which the ammonia levels are zero.

A good source of bacteria is either a scoop of surface gravel or some bio media from the filter of an established healthy aquarium, as long as the aquarium has not been treated with medications or other chemicals. Another choice is a bacteria additive.

Once the bacteria have become established in the biological media, they are difficult to destroy, except by over-cleaning, using chlorinated water, or using certain medications.

A variety of media is available for bacteria housing. Small biological media are extremely porous and boast incredible surface areas. They can accommodate a lot of bacteria in a small space. They also can get clogged easily, and lose their effectiveness quickly if inadequate mechanical filtration is used. Smaller media last 2-4 years, and are an excellent option if you have a small tank. Plastic media do not have the extensive surface area, but they are unlikely to clog and never need replacing.

Note: Biological media houses the natural bacteria involved in the nitrogen cycle. It provides a larger surface area for beneficial bacteria to colonize, allowing water can pass over the colonies, bringing nutrients and oxygen required for the nitrogen cycle.

Chemical media

Chemical media is not used as often as biological or mechanical media, but can be effective for an assortment of filtering purposes. This media is available in a variety of materials that can remove one impurity or many.

The chemical method of filtration removes dissolved particulates from the aquarium via activated carbons, resins, and other adsorbents. Chemical filtration media helps to maintain water quality as unwanted dissolved matter adheres to it. The two most popular forms of chemical media are activated carbon and resins. Protein foam skimming or oxidation with ozone are two other forms of chemical filtration.

Activated carbon

Carbon is filled with microscopic pores that allow certain organic or inorganic materials to stick to them. New carbon works more efficiently than older carbon. When all of the pores are filled, the carbon is no longer effective and the filter begins to act as a biological filter.

Carbon removes many harmful elements from your aquarium, such as: copper, chlorine, dissolved proteins, and carbohydrates. It also removes sulfa drugs and antibiotics, so it should be removed when the aquarium is being treated, then replaced when treatment is completed to remove any leftover medications. Activated carbon can make your aquarium look so clear by removing discolorants that you will question whether water is still in it.

Ion exchange resins

Resins are less utilized than carbon, but are becoming more common. These work by attracting a specific molecule to adhere to them. Some attract ammonia or nitrate, and some remove dissolved organics. Ion exchange resins are also utilized in some carbon mixtures like Chemi-Pure and Bio Chem Zorb. The resins often strengthen the filtering ability of the carbon, as well as help biological activity by removing pollutants before they enter the nitrogen cycle. Used properly, chemical filtration can be one of the most useful tools of the aquarist.


When designing your aquarium, give careful consideration to the types of filters and filter media you will use. Your choices can make the difference between a healthy ecosystem or one in which the inhabitants must struggle daily to survive.

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