Mechanical filter media removes unsightly particles from the aquarium. This may include 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.