Support Gravel, the lower part of your filtration system, supports the water filtration media for various systems such as Carbon Filtration Systems, pH Neutralizers, Birm, Greensand and Greensand Plus, Katalox, Pyrolox and Filter-Ag

**NOTE: YOU DO NOT USE THIS ENTIRE BAG IN ONE TANK. YOU ONLY NEED ABOUT 16 POUNDS TO LINE THE BOTTOM OF EACH OF YOUR WATER FILTRATION SYSTEM TANKS.