Our Granular Activated Carbon (GAC) is a special grade bituminous carbon, liquid phase activated, made specifically for aquarium use. It has a larger pore structure than typical bituminous carbons, making it more like lignite, but slightly harder and with less dust. The larger particle size at 4x12 mesh, makes it an ideal carbon to be used in media reactors, mesh bags, or cartridges. Produced entirely in the USA, it contains zero contaminants and will not leach phosphate into your water.