Black Diamond Premium Activated Carbon eliminates foul odors, unsightly discoloration and harmful organic substances for freshwater or marine aquarium filtration. Heat activated bituminous coal based granules are specially sized (won't damage filter impellers). With Black Diamond Premium activated carbon, you also get more carbon. As much as 60% of other prewashed activated carbon weight is water, not carbon. Black Diamond Premium Activated Carbon contains less than 2% moisture, and is phosphate free.