Onyx Sandâ„¢ is a naturally dark gray sand that perfectly complements and enhances the appearance of any aquarium. It supports optimal KH levels for freshwater planted aquariums. Although ideally suited to planted aquaria, it may be used in any aquarium environment. Onyx Sandâ„¢ is most effective when used alone as an integral substrate bed, but it may be mixed with other gravels. Gravel modifiers such as laterite are not necessary. Onyx Sandâ„¢ is not chemically coated or treated, and as a carbonate rich sand, it has a slight buffering capacity that may raise pH by 0.1 - 0.5 pH units (depending on source water characteristics). Onyx Sandâ„¢ is good for the life of the aquarium and need not be replaced.