The only crushed coral with aragonite, which provides up to 25 times the buffering power of other crushed corals, dolomite, or oyster shell. Will eliminate chronic pH problems and provide maximum surface area for water purifying bacteria. Allows an increase in bioload by up to 50% and it will never need to be replaced. Can be used with calcium, but also carbonate buffer and essential trace elements such as strontium (up to 10,000 ppm). Mixed Grade. Grain size: 2.0 -5.5mm.