A complete reactor media containing not only calcium and carbonate,but essential trace elements as well. in face,ARM has nearly 50 time the strontium of outher brands (7390 ppm).ARM is processed for immediate use with no rinsing required,and has double the surface area of regular aragonite.Calcium reacotors have evolved into several types that require different media size.We now offer our orignal ARM fine for downflow,slow upflow,and fluidzed bed type calcium reactors and our ARM coarse for rapid upflow type reactors.No matter the reactor,Caribsea has you covered.