ahhhhh are you talking about carbon???
Carbon is filled with microscopic pores that cause certain organic or inorganic materials to stick to them. New carbon works more efficiently than older carbon. When all of the pores are filled, the carbon is no longer effective and the filter begins to act as a biological filter. 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 treated, then replaced when treatment is completed to remove any leftover medications. Activated carbon can make your aquarium look so clear by removing discolorants that you'll question whether water is still in it.