The perfect shell substrate, Clean and pure with no dangerous impurities to threaten your aquarium, May be used on it"s own or as a colorful ad mixture to other products, Caribbean sea Aruba shells offer buffering capabilities that are superior to oyster shell coquina shell calcite dolomite and most varieties of beach collected shell, Natural and free from impurities, Actual sea floor mix of sand and shells, SKU: RYLHC1137