Canister-filter.com

Chemical filtration is most often used to get rid of ammonia and other polutants from the aquarium water. Activated carbon is the most well know material to use for chemical filtration. There are other substances like zeolite and peat.

Activated carbon basically holds on to the polutants like ammonia. The ammonia however is not converted and there's always a chance that it will be reintroduced in to the system. Besides this, the carbon can only hold a certain load of polutants. This means that you have to refresh the carbon on a regular basis depending on the situation of your aquarium.

The activated carbon will also extract any odors but can have some negative side effects aswell. Change of Ph level or adding phosphates for example. Stick by the rule that this goes for any chemical filtration material that you introduce to your canister filter and be advised.