FIVE PACK. Each is 4" X 8" size. The Poly-Bio-Marine Poly Filters are a formulation of a special patented material bonded to a synthetic matrix. By means of a unique proprietary process, the Poly Filter is made impervious to salt and is also organic loving to certain materials. The Poly Filter pads absorb and adsorb contaminants and other toxic materials found in nature or added to fresh and salt water with or without fish and invertebrates. Medication added to aquariums for treatment of diseased fish will automatically be removed by the Poly Filter (after serving their intended purpose). It provides a supplemental means for removal of ammonia when the biological filter is unable to break down the excess ammonia and its concentration increases rapidly.