ARM Extra Coarse 3.8L

A complete reactor media containing not only calcium and
  carbonate, but essential trace elements as well. In fact A.R.M. has nearly 50
  times the strontium of other brands (7,390 ppm) A.R.M. is processed for
  immediate use, no rinsing required, and has double the surface area of
  regular aragonite. Precision grading (2-3mm) allows for maximum carbon
  dioxide penetration.