CaribSea's Geo-Marine Florida Crushed Coral is the only crushed coral with aragonite and provides over 25 times the buffering capacity of other crushed corals. In actuality, this product is not crushed at all, but is a natural product that is screened to size. The unbelievably natural substrate provides dramatic color and texture to your aquarium environment and combines well with fine reef sand offering creatures such as jawfish, blennies and burrowing crustaceans an opportunity to dig, burrow and create their own unique homes. Due to the fact that the Coraline Caribbean Crushed Coral substrate is so coarse, it makes an excellent choice for systems that feature undergravel filtration or where elevated pH levels are required. The substrate has been purposely engineered and is free of impurities such as ash, metals, pesticides, and silica; which allows you to create a safe and beautiful environment for your fish and invertebrates. Can be used alone or as a textural admixture. The 10 pound bag features a typical size between 2.5 mm and 5.5 mm and has an average density of 72 pounds per cubic foot.