The three main types of filter media are:

1. Mechanical
2. Biological
3. Chemical

Mechanical filter media removes unsightly particles from the aquarium including fish excrement, sludge, uneaten food, or dust. Aquarium water is passed through a mechanical filter media, and the particles are strained out. To prevent build-up, the filter media must be cleaned regularly.

The components of mechanical media are inert - this means that the material this media is made of 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. It simply needs to be cleaned - replacement is only required when it can no longer release all the dirt that it holds.

Mechanical media is available in many different porosities, which control the size of the particulate that you 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. This type of 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 aquarium, but will clog very quickly, and may not be reusable.

Media	What Grade	Usage
Coarse 1" Thick Mechanical Filter Media Pads	Very coarse	Catches large debris so that small media doesn't need to be cleaned as often.
Blue bonded Filter pads, or foam blocks	Coarse to medium	Cleans most visible debris.
Filter floss	Fine	Filters out fine particles providing crystal clear water.
	Extra Fine	Removes extra small particulate, even parasites and bacteria.

Biological media is anything inert that provides housing for nitrifying bacteria that break down nitrogenous pollutants 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 how nitrifying bacteria thrive:

• Environment above 55°F
• Need ammonia or nitrite as food source
• Need oxygen for life

Nitrifying bacteria extract oxygen from water moving by them. If particulate matter gets into the media and decreases water flow, it "starves" that area of oxygen and food, causing nitrifying bacteria to die in that area. This is why mechanical media is suggested before biological media.

When the bio load increases, the abundance of ammonia and nitrite causes the bacteria to reproduce. Nitrifying bacteria that consume ammonia reproduce quickly, until the ammonia level drops to zero. Sometimes, they over-produce and cause a "bacteria bloom" that gives the aquarium a cloudy or smoky appearance. Once the correct number of bacteria have grown to overcome the ammonia spike, the excess bacteria starve and die, and the cloudy tank water disappears.

In an established aquarium, 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 aquariums, the time the ammonia takes to be converted by bacteria depends on the amount of fish load and bacteria.

Biological media houses bacteria involved in the nitrogen cycle. It provides a larger surface area for beneficial nitrifying bacteria to colonize, where water can pass through the colonies, bringing nutrients and oxygen required for the nitrogen cycle.

A useful source of bacteria is a scoop of surface gravel from an established healthy aquarium or some bio media from the filter, as long as the aquarium hasn't 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.

As the ammonia-eating bacteria consume ammonia, they give off nitrite, and then in come the nitrite-eating bacteria. These bacteria are slower to reproduce, preferring to wait until ammonia levels are zero.

A variety of media is available for housing bacteria. 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 limited amount of space in your filter. Plastic media, such as bio balls, do not have the extensive surface area, but they are unlikely to clog and never need replacing.

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.

Chemical media such as Poly Filter, are effective at removing a variety of impurities such as copper, chlorine, dissolved proteins, medications, or tap water impurities by binding these unwanted materials and trapping them within the media.

Activated carbon, resins, and other adsorbent chemical media bind and remove dissolved particulates from the water column through the process of adsorption. The two most popular forms of chemical media are activated carbon and resins.

Activated Carbon - Activated Carbon is filled with microscopic pores that cause certain organic or inorganic materials to stick to them. Fresh carbon works more efficiently than older carbon. When all the pores are filled, the carbon is no longer effective.

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 medicated, then replaced when treatment is completed to remove any leftover medications. Activated carbon is also extremely efficient at removing water discoloration. In other words, activated carbon can eliminate unsightly murky or cloudy tank water conditions, making your aquarium look so clear that you'll question whether water is still in it.

Ion exchange resins - These filter media are less utilized than carbon but are becoming more popular. 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. 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.