Seahorse aquariums are please to now offer a huge range of coloured and natural gravels for freshwater aquariums. All of these gravels are pH balanced and rounded off by nature. The gravel is somewhat porous, that even lets the hair roots of plants grow along the gravels. All coloured gravels must be rinsed in cold water before use. Coloured gravels can not be placed in water over 35 degrees in temperature. All coloured gravels are non toxic to fish, plants and invertebrates.