Filter Media
Mechanical Filters: are used to trap solid waste.

Chemical Filters: are used to remove chemicals or metals, or add chemicals.

Biological Filters: are used to grow colonies of nitrifying bacteria.

The filter media described below can be used in almost any type of canister or box filter that doesn't require specifically shaped filter media.

Carbon
Carbon is a chemical filter media, It will remove medications and heavy metals from the water. It will not remove ammonia, nitrite or nitrate. Carbon works by absorbing contaminants on its surfaces which means the amount it can absorb is limited. So the carbon media has to be replaced at regular intervals. Cheap carbon media is made from charcoal, more expensive carbon media is made from coal or coconut shells which gives the charcoal an increased total surface area allowing it to absorb even more contaminants. Before adding new carbon media it should be rinsed to remove small loose particles of carbon.
Foam
Foam is a very effective mechanical and bioloical filter media. They can be purchased in specifically shaped forms to fit different filters. Only foam made for aquariums should be used because other foams can contain toxins. Foam can be cleaned and reused many times, but will need to be replaced in time because they do start to deteriorate.
Floss (Filter Wool)
Floss is a cheap and a effective mechanical and bioloical filter media. It is used as a pre-filter, to catch any small particles of waste, this helps prevent other media in a filter clogging up with dirt. Floss gets dirty and clogged very quickly, it should be replaced on a weekly basis.
Ceramics
Ceramic media is available in many different shapes, but is normally shaped into hollow tubes, ceramic media is a mechanical and bioloical filter media. Ceramic media doesn't clog up easily and allows water to flow freely which means this medium is often placed first in a filter. Ceramics can be washed and reused.
Sintered Glass
Sintered glass is highly porous,1 litre Sintered glass provides as much bacteria settling area as 34 litres of ceramic filter materials. Thus making it a very efficient biological medium. But it can clog up very quickly, so it would be wise to use floss in front of sintered glass to prevent it clogging up.
Zeolite
Zeolite is a ion-exchange resin which neutralises ammonia. Zeolite is a chemical filter medium. Zeolite has a limited capacity, but it can be reused after soaking it in salt water for 24 hours and then cleaning with fresh water. Zeolite should only used in emergencies where temporary high ammonia problems occur.
Gravel
Any type or size of aquarium gravel can be used as mechanical and bioloical medium. Sand is not suitable because it compacts down and clogs up, which can create anaerobic conditions. Gravel may also be a chemical medium unless it is a pH-neutral gravel. Gravel can be washed and re-used.
Peat
Peat acts as a chemical medium but can also be a mechanical and bioloical medium. Peat is used to reduce the pH level in aquarium water for acid-water fish. Peat should be used in a nylon media bag to stop it escaping into the aquarium. Peat should be rinsed to release any small particles before using it. The tannins released from peat makes aquarium water turn a tea-colour.
Calcium Carbonate
Calcium Carbonate acts as a chemical medium but can also be a mechanical and bioloical medium. Calcium Carbonate is used to increase the pH level in aquarium water for hard-water fish. Coral gravel, coral sand, limestone gravel and marble chips all contain calcium carbonate. These materials should be rinsed before being used and they can also be washed and re-used.