Reef Ground Sand 0.5 - 1.2 mm dia., 20 KGSize: 20 KG Ultrapure natural aragonite of fossil origin as a substrate for all marine water aquaria. Due to its purity, extremely bright with high light reflectance which is particularly an advantage for light hungry corals. Reef Ground is an outstanding alternative to natural coral sand and protects the environment. Before placing in the aquarium, rinse the substrate thoroughly. CaCO3 99. 2% MgCO3 0. 4% FeO3 0. 035 %