One 20-count bag should be used for every 100 u. s. gallons. Grows massive colonies of beneficial bacteria. Provides more growing area than plastic balls, foam, or undergravel fillers. Allows best oxygen and water transfer, for best bacterial health. Biological Filtration Medium That Provides A Substrate For Optimal Growth Of Beneficial Bacteria. The Internal Pore Structure Is Formed Under A Patented Process That Creates A 50 To 70 Micron Pore Network, Which Is Optimal For Beneficial Bacteria. 20 COUNT