High quality natural substrate for planted aquarium. Good for the aquarium. Provides essential minerals for plant growth. Flourite Dark is a stable porous clay gravel specially ground for the natural planted aquarium. Its appearance is best suited for planted aquariums, but can be used in any freshwater aquarium environment. Flourite Dark is most effective when used alone as an integral substrate bed, but can be mixed with other gravels. Flourite gravel is not dyed or chemically treated and does not alter the pH of the water. Flourite Red is good for the aquarium and does not need to be replaced.