FlouriteÂ® Dark is a specially fracted stable porous clay gravel for the natural planted aquarium. Its appearance is best suited to planted aquaria, but may be used in any freshwater aquarium environment. FlouriteÂ® Dark 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. FlouriteÂ® Dark is not chemically coated or treated and will not alter the pH of the water. FlouriteÂ® Dark is good for the life of the aquarium and need not be replaced.