The Reef Octopus CR100 4-Inch Calcium Reactor is the entry point to the Classic calcium reactor line, using a reverse-flow design to maximize contact time between aquarium water, pressurized CO2, and aragonite media. As CO2 lowers the pH inside the chamber, the aragonite dissolves and releases calcium, alkalinity, and trace elements back into the water — a largely automated way to keep up with coral demand. Best for: hobbyist reef tanks wanting automated calcium/alkalinity dosing Body: 4-inch reaction chamber, reverse-flow design Monitoring: built-in pH probe holder and bubble counter for tracking CO2 drip rate (pH probe and controller sold separately) A calcium reactor is the lowest-maintenance way to keep pace with SPS-heavy or otherwise calcium-hungry systems — once dialed in, it needs far less manual dosing than liquid two-part supplements.Compatible replacement parts: media chamber seals and bubble counters for the CR100.
