Red Sea Fish Pharm ARE40261 Max Filter Sponge Media for Aquarium Filter Matrix Carbon Is A Truly Unique Activated Carbon It Is Formed As A Spherical Bead For Optimum Hydrodynamics And Will Not Pack Permits maximum water flow and contact with its high density of macro porous binding sites Matrix Carbon Has A Very Low Ash Content As Indicated By Its Minimal Impact On Ph Even When Added To Distilled Water, It Does Not Raise Ph Above 7.0