Octo CalReact 5000D Dual Chamber Calcium Reactor

OCTO CalReact 5000D Dual-Chamber Calcium Reactor

The OCTO CalReact 5000D is Reef Octopus's flagship calcium reactor, engineered for large reef systems that demand reliable, automated calcium and alkalinity supplementation at scale. With a 15.2-liter media capacity and a rated tank range of 423 to 608 gallons, the CalReact 5000D handles the sustained mineral demand of heavily stocked SPS and mixed-reef systems where two-part dosing or kalkwasser can't keep pace.

At the core of the design is a dual-chamber, reverse-flow CO2 recirculation system. Aquarium water and CO2 enter the reaction chamber, where the reverse-flow configuration keeps CO2 circulating through the aragonite media rather than allowing it to escape prematurely. The result is a more thorough dissolution of calcium, magnesium, and trace elements with less CO2 waste. The integrated bubble counter makes it straightforward to dial in the CO2 drip rate, and the pH probe holder (probe sold separately) allows continuous monitoring of effluent alkalinity, enabling the reactor to be run in closed loop with an external controller.

Circulation is handled by the VarioS 6 DC pump. The same variable-speed platform is used across Reef Octopus's professional skimmer line. Running at 70W with a maximum flow rate of 6,500 L/h (1,720 gph) and a 4.9m (16 ft) max head height, the VarioS 6 gives the hobbyist precise control over recirculation speed without the noise or inefficiency of a fixed-speed AC pump. The removable lid simplifies media top-offs and chamber maintenance, and the hand-cast solid acrylic body is built to the same construction standard as Reef Octopus's protein skimmer line. 

Key Features:

• Dual-chamber, reverse-flow CO2 recirculation system extends contact time with aragonite media, improving dissolution efficiency and reducing CO2 consumption
• 15.2L (4.0 gal) media capacity supports sustained supplementation for large, high-demand reef systems without frequent top-offs
• VarioS 6 DC pump operates at variable speed via detachable controller — adjustable flow from low to 6,500 L/h (1,720 gph) to match tank demand
• Built-in bubble counter for direct, visual monitoring of CO2 drip rate without external accessories
• pH probe holder accommodates a standard probe (sold separately) for continuous effluent monitoring and compatibility with external pH controllers
• Removable lid provides full access to the reaction chamber for media loading and routine maintenance
• Hand-cast solid acrylic body construction — same material standard as Reef Octopus's protein skimmer line
• Compatible with both wet and dry installation configurations; inlet/outlet: 6.3mm (¼ inch)

Ideal For:

• Large mixed-reef aquariums in the 420–600+ gallon range where consistent calcium and alkalinity demand exceeds what two-part or kalkwasser can practically provide
• SPS-dominant systems with high and consistent calcium draw that benefit from automated, stable supplementation rather than manual dosing adjustments
• Reef systems experiencing frequent two-part depletion or kalkwasser saturation limits and ready to transition to a reactor-based approach
• Multi-tank or system-fed installations where a single high-capacity reactor can serve shared water volume
• Hobbyists scaling up from a smaller reactor (such as the CalReact 3000D) as coral biomass and mineral demand have grown

What's Included:

• Reaction chamber (dual-chamber, hand-cast acrylic)
• Main chamber cover (x1)
• Second chamber cover (x1)
• VarioS 6 DC circulation pump with detachable controller
• Pump union fitting pH probe holder (probe not included)
• Bracket (x1) Sponge media filter pads (x4)
• Cross connection fitting (x1)
• CO2 check valve (x1)
• Effluent control valve (x1)
• Inlet/outlet valves (x2)
• CO2 inlet valve (x1)
• Inlet/outlet fitting (x1)
• Rubber shim (x1)
• O-rings (x3, assorted) 

Specifications:

• Model: CalReact 5000D
• Configuration: Dual-chamber, reverse-flow CO2 recirculation
• Media Capacity: 15.2 L / 4.0 US gal
• Recommended Tank Volume: 1,600–2,300 L / 423–608 US gal
• Reactor Diameter: 200 mm / 7.9 in
• Footprint: 460 mm × 385 mm / 18.1 in × 15.2 in
• Height: 580 mm / 22.9 in
• Inlet/Outlet Size: Ø 6.3 mm (¼ in)
• Pump: VarioS 6 DC (variable speed, detachable controller)
• Pump Power: 70W
• Pump Max Flow Rate: 6,500 L/h / 1,720 gph
• Pump Max Head Height: 4.9 m / 16.0 ft
• Suggested Feed Pump Flow: 500–800 L/h / 132–211 gph
• Operating Mode: Wet or dry installation
• Body Material: Hand-cast solid acrylic
• pH Probe Included: No (probe holder included; probe sold separately)
• Aragonite: Not included