Reef Ground Sand 0.5 - 1.2 mm dia., 3 LSize: 3 L Highly pure, natural aragonite of fossil origin as a soil substrate for all saltwater aquariums. Extremely bright with high light reflection due to the purity, which is particularly advantageous for light hungry corals. Reef Ground is an excellent alternative to natural coral sand and respects the environment. Before bringing them into the aquarium, the substrate should be washed thoroughly. CaCO 3 99. 2% MgCO 3 0. 4% FeO 3 0. 035%