ARM™ Fine is for most downflow reactors, fludized bed type reactors, and all uplflow reactors other than rapid upflow type. It is a complete reactor media containing not only calcium and carbonate, but essential trace elements as well. In fact, ARM™ has nearly 50 times the strontium of other brands (7390 ppm). ARM™ 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, and the exclusion of gastropod shells insures the lowest phosphate (less than 1/10 of 1 ppm) content. This grading also carries in the highest concentration of Halimeda incrassata, an aragonite so pure it has been used as a laboratory standard. ARM™ has the highest solubility of any reactor media available (metastable at 8.2) so typical CO2 consumption is much lower.