Processed, porous, highly adsorptive form of carbon also known as activated charcoal or active carbon. Used in aquaria to remove toxins such as chlorine, chloramine, some heavy metals, and especially organic molecules, but exerts no action on ammonia, nitrite, nitrate, phosphate or inorganic salts. Since it has a finite surface area it requires periodic replacement if employed long-term, and should be removed if a tank is being treated as it will remove most medications. Cannot be ‘recharged’ by heating in a microwave or domestic oven.