Caribbean Crushed Coral is full of millions of bacteria that are beneficial to any marine aquarium, engineered for aggressive waste reduction. With the ability to compress ammonia, in new tanks it is proven to help cycle the aquarium days earlier. 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. The 20 pound bag features a typical size between 3.0 mm and 6.0 mm and has an average density of 72 pounds per cubic foot.