Dymax Volcanic Media is a natural biological filtration material. The rough surface area allows increased adhesion for bacteria while ensuring the rapid decomposition of harmful substances. With its fast action of decomposition this media is extremely effective for even large scale aquarium filtration systems. eg. koi pond and marine aquarium etc. The Dymax Volcanic media is specially developed to offer optimum biological filtration for your aquarium compared to other media. Helps to remove nitrate.