Fiji Pink Reef Sand: 0.5-1.5 mm diameter grain size. A gently hued aragonite, CaribSea Seaflor Pink Fiji Reef Sand is ideal for plenum systems, nitrate reduction systems and most fish and reef tanks. Helps achieve the pH of natural seawater. Proves calcium and other essential trace elements like strontium and magnesium. CaribSea Aragonite buffers to the highest pH and delivers more calcium, carbonate, and trace elements than any other substrate. Little or no rinsing required, aragonite keeps aquariums healthier, longer.