Clack Garnet is a high hardness, high density granular filter media. It is normally used as the lower (final) filtration in a multi-media bed down flow filtration system.
Called multi-media or mixed media filtration, the high density, small grain size of Clack #30-40 Garnet solves a major filtration problem. In a single media granular filter such as a sand filter, the material will hydraulically classify during backwash according to granule size, the smallest rising to the top. When water flows downward through the sand, the fine particles at the top of the bed do most of the straining of the sediment. The solids form a cake on the surface with filtration typically taking place in the top few inches. As the cake forms, the filtration becomes finer and the head loss increases exponentially with time.
#8 Garnet at 140 lb/ ft³ is a good choice for support beds when using other high density filtration media such as high purity Corosex II or the new manganese dioxide oxidation medias such as Pyrolox.