Nature's Ocean Samoa Pink Gravel#2 20LBS Premium Aragonite Reef Substrate: Ideal for reef system tank bottoms, denitrifying anaerobic beds, extremely high surface area filter media. Aragonite Benefits: Reduces Nitrates. Maintain pH. Increases Carbonate Hardness. Provide Marine Trace Elements. Pre-washed Minimum Rinse Required. 100% From The Ocean Floor. Heat Sterilized. Ideal for culturing Live sand.