Caribsea ARM COARSE Calcium Reactor Media 8 lbs.Calcium reactors have evolved into several types that require different media sizes. We now offer our original ARM fine for down-flow, slow up-flow, and fluidized bed type calcium reactors and our ARM coarse for rapid up-flow type reactors…Caribsea ARM COARSE Calcium Reactor Media 8 lbs. Calcium reactors have evolved into several types that require different media sizes. We now offer our original ARM fine for down-flow, slow up-flow, and fluidized bed type calcium reactors and our ARM coarse for rapid up-flow type reactors. No matter the reactor, CaribSea has you covered.Product code: 1234Item No. CR-ARM-LG