Calcium reactor

In marine and reef aquariums, a calcium reactor is a device used to create a balance of alkalinity in the system. An acidic solution is produced by injecting carbon dioxide into a chamber with salt water and calcium rich media. The carbon dioxide lowers the pH, dissolving the calcium media, and producing a solution high in carboxylic acid. The effluent is then returned to the reef aquarium where the calcium is consumed by organisms, primarily corals when building skeletons. A calcium reactor is one of the most efficient methods of supplying calcium to a reef aquarium.

Reaction

The objective is to dissolve the calcium laden media to provide both bicarbonates HCO₃^- (alkalinity) and calcium (Ca⁺⁺) ions at the sames rate as consumed during calcification. Effectively dissolving the media requires an acidic pH. Saltwater typically has a pH of at least 8.0, so to reduce the pH carbon dioxide (CO₂) is used. The general reaction form is:

CaCO₃ + H₂O + CO₂ <——> Ca²⁺ + 2HCO₃^-

Design and operation

CO₂ Chamber

Inside the reaction chamber, a calcium rich media, mainly CaCO₃, is forced into contact with water injected with carbon dioxide (CO₂) in order to create carbonic acid(H₂CO₃). This increases the solubility of the calcium carbonate. The reaction free the calcium and carbonate, supplying the aquarium with water rich in Ca²⁺ and CO₃^2-, important for maintaining both alkalinity and calcium levels.

Bubble Counter

The bubble counter is used to measure the rate of carbon dioxide introduced to the system. The flow rate of carbon dioxide must be monitored so that the maximum amount of gas dissolves into the solution with a minimum left unconsumed. A needle valve is used to regulate the CO₂ bubble rate. Valves with precise adjustment abilities will improve bubble control characteristics.

Feed Pump

The feed pump controls the volume of water exchange in the system. This is important because a high rate of water flow into the reactor reduces it's efficiency, thus resulting in underproduction and a waste of CO₂.

A number of methods exist to supply the reactor with water from the tank. Some reactors siphon water into the input of the reactor's re-circulation pump. A potential complication is the medium in the reactor becoming compacted, increasing back pressure onto the pump and reducing water into the reactor. Placing a gate or needle valve on the reactor's outlet side will improve flow characteristics compared to control from the inlet side.

Alternately, peristaltic pumps are effective operating against pressure, capable of supplying a precisely adjustable and continuous flow over a variety of flow rates with minimal maintenance.

pH Control

The pH control is connected to a probe in the reactor and adjusts the rate at which the calcium media dissolves. When the pH rises above a certain level, a valve opens, allowing carbon dioxide to enter the reactor. The control also closes the valve as the pH falls below this level.

ee also

* Aquarium
* Protein skimmer
* Filter

References

* [http://reefkeeping.com/issues/2002-05/sh/feature/index.php Reefkeeping.com article on calcium reactors]
* [http://avdil.gtri.gatech.edu/RCM/RCM/Aquarium/CalciumReactor.html Georgia Tech information on calcium reactor]

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