Premium Atlantic Crushed Coral Sand with Aragonite #1 is comprised of crushed natural coral from the ocean floor, pre-washed for convenience. It maintains superior pH and marine chemical balance. Uniformally size to provide maximum surface area for biological nitrification, water flow and aeration to prevent anaerobic "dead spots" in the bacteria bed. An attractive and chemical free way to improve your aquarium's quality. Premium Atlantic Crushed Coral Sand with Aragonite #1 features 1.2 to 1.7 mm grain size.