Selecting and cleaning the filter media in your filter system is important in maintaining a healthy aquarium. The filter media is in constant contact with the water in your aquarium and have an important role to play. The first type of filter media is designed to perform mechanical filtration and is designed to remove particles and make the water clearer. The second type of filter media is biological and is designed to remove harmful compounds that if leave untreated would kill your fish. The last type of filter media is chemical and is design to remove harmful chemicals.