The Reef Octopus SRO CR5000D 8-Inch Dual Chamber Calcium Reactor is the largest fixed-speed calcium reactor in the SRO line, running two 8-inch chambers in series for maximum dissolution efficiency on demanding systems. A high water volume Water Blaster pump with silicone-carbide shaft and bearings drives reverse-flow circulation. Body: dual 8-inch reaction chambers in series Pump: Water Blaster recirculation pump, reverse-flow design, 2-year pump warranty Monitoring: pH probe holder in the first chamber, built-in bubble counter For calcium-loving reef systems with heavy coral stocking, the dual 8-inch chambers give this reactor the largest media capacity in the fixed-speed SRO calcium reactor lineup.Compatible replacement parts: Water Blaster pump kits for the CR5000D.