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