ReefPure Granular Activated Carbon is a unique lignite based media designed specifically for high purity saltwater purification. It efficiently removes harmful organic compounds, yellowing substances, medications and organic acids. In addition it has a macroporous structure allowing adsorption of the large organic molecules we're concerned with in the marine and reef aquarium. ReefPure GAC will not remove critical trace elements or affect pH like lower quality competing products. ReefPure GAC will produce sparkling clear water allowing more light to penetrate the water and reach your corals. ReefPure GAC is far superior to the "pelleted" type GAC found in lower quality competing products. Those products have very little ability to adsorb and should be avoided.