Flourite® 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. Flourite® 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. If mixed with other gravels, your mixture must contain 50% of Flourite® . This product Flourite® Dark is not chemically coated or treated and will not alter the pH of the water. Flourite® Dark is good for the life of the aquarium and need not be replaced.