Reef Endurance Small Calcium Reactor Media 16kg (35.2lbs) BoxSmall Granule Aragonite Media from sustainably harvested fossil corals. Average grain size: 3 4mm. Replenishes Calcium, Carbonate Alkalinity, and Essential Trace Elements Reef Endurance calcium reactor media is natural aragonite rubble from sustainably harvested fossil corals, collected and cleaned for use as the sole media for calcium reactors to support rapid coral growth. Small 3 4mm rubble is the ideal grain size for small calcium reactors and a