Onyx™ is a specially fracted natural substrate for the aquarium. Onyx™ is suitable for any marine or freshwater environments and is ideally suited for Cichlid environments. Onyx™ is most effective when used alone as an integral substrate bed, but it may be mixed with other gravels or sands such as Onyx Sand™. Onyx™ is not chemically coated or treated but does have a slight buffering capacity.