The main content of Aquarium Calcium Sand is calcium carbonate  which is the same composition as coral sand，It is the best substitute for coral sand for aquarium tank landscaping. the soluble calcium, carbonate and trace elements can be precipitated slowly in the aquarium tank,It is used to supplement the needs of marine organisms and increase KH and stabilize PH. the porous structure of calcium sand can promote the osmotic dissolution of carbon dioxide (CO₂）,Calcium sand have different sizes for various aquarium tanks. Clean it with clean water before use and then put it into tank.