Caribsea Florida Crushed Coral 10 lb. bag, aragonite based, helps maintain pH to 8.3. It's the only crushed coral with aragonite, which provides up to 25 times the buffering power of other crushed corals, dolomite or oyster shell. Eliminate chronic pH problems and provide maximum surface area for water purifying bacteria. CaribSea's Florida Crushed Coral with aragonite allows an increase in bioload by up to 50% and it never needs replacement! Approx. 2 - 5mm diameter (1/8 - 1/4 in.). This product is also able to be utilized in calcium reactors and plenum systems to deliver not only calcium, but also carbonate buffer, and essential trace elements such as strontium (up to 10,000 ppm!).