__NOTOC__ A calcium reactor is an efficient method to supply calcium and trace elements to a reef aquarium. Reactors may be used in elaborate

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

and brackish aquariums where freshwater clams and other

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

need a constant supply of

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

. In marine and

reef aquarium A reef aquarium or reef tank is a marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the tropical coral reef environment. A reef aquarium requires appropriately i ...

s, a calcium reactor dissolves a calcium carbonate media in order to balance

alkalinity Alkalinity (from ) is the capacity of water to resist Freshwater acidification, acidification. It should not be confused with base (chemistry), basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer s ...

and introduce other trace elements. An acidic solution is produced by injecting

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

into a reaction chamber with salt water and

rich media. The carbon dioxide lowers the pH by producing a solution high in

carbonic acid Carbonic acid is a chemical compound with the chemical formula . The molecule rapidly converts to water and carbon dioxide in the presence of water. However, in the absence of water, it is quite stable at room temperature. The interconversion ...

, and dissolves calcium. This solution is recirculated through the reaction chamber via a recirculating pump. The effluent, which is now rich in elements from the dissolved media, is returned to the

where the elements are consumed by organisms, primarily

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

s when building skeletons. The reactor dissolves the calcium-laden media to provide bicarbonates HCO₃⁻ (alkalinity) and calcium (Ca⁺⁺) ions at the same rate as consumed during calcification. Effectively dissolving the media requires an acidic pH. Saltwater may have a pH of 7.8 or higher, so to reduce the pH carbon dioxide (CO₂) is used. The reaction formula is: : CaCO₃ + H₂O + CO₂ ⟷ Ca²⁺ + 2 HCO₃⁻ Inside the reaction chamber, a calcium rich media (

aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...

), mainly CaCO₃, is forced into contact with water injected with

(CO₂) in order to create

(H₂CO₃). This increases the solubility of the

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

. The reaction frees the calcium and carbonate, supplying the aquarium with water rich in Ca²⁺ and CO₃²⁻, important for maintaining alkalinity and calcium levels. A bubble counter is used to visually (or audibly) measure the carbon dioxide rate (bubbles per minute). The flow rate of carbon dioxide is monitored so that the dissolved gas goes into the solution, with a minimum unconsumed. A

needle valve A needle valve is a type of valve with a small port and a screw thread, threaded, needle-shaped plunger. It allows wikt:precision, precise regulation of Fluid dynamics, flow, although it is generally only capable of relatively low flow rates. ...

solenoid valve A solenoid valve is an electromechanically operated valve. Solenoid valves differ in the characteristics of the electric current they use, the strength of the magnetic field they generate, the mechanism they use to regulate the fluid, and the ...

generally attached to the CO2 regulator regulates the CO₂ bubble rate. Valves with precise adjustment abilities improve bubble control. A feed pump takes aquarium water into the reactor, controlling the volume of water exchange. This is important because a high rate of water flow into the reactor can reduce its efficiency, thus resulting in underproduction and a waste of CO₂. 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.

Peristaltic pump A peristaltic pump, also commonly known as a roller pump, is a type of positive displacement pump used for pumping a variety of fluids. The fluid is contained in a flexible tube fitted inside a circular pump casing. Most peristaltic pumps work th ...

s are effective operating against pressure, capable of supplying an adjustable and continuous flow over flow rates with minimal maintenance. A pH controller is recommended to control the CO2. It works by connecting to the CO2 regulator on the CO2 tank and measuring the pH of the solution inside the reactor via a pH probe. The controller will turn on and off the flow of CO2 based on the pH inside the reactor. The pH range for the typical calcium reactor is 6.5–6.8. When the pH rises above a certain level, a valve opens, allowing carbon dioxide to enter the reactor. The controller closes the valve as the pH falls below this level. MRC-CR4

Some pH controllers have an interface for an air pump. This air pump is connected to an airstone in the sump or main tank. If the probe detects a low pH level, the pump activates. The bubbles raise the pH by dissipating the CO₂ gas. Since the pH inside the reactor is much lower than the pH in the aquarium, you run the risk of lowering the aquarium pH by running a calcium reactor if that low pH isn't mitigated. To counteract that effect, many manufacturers offer reactors with secondary buffering chambers. This buffering chamber is filled with the same media as the primary chamber, however, no CO2 is injected into this chamber. The effluent of the primary chamber passes through the buffering chamber, consuming any excess CO2 and raising the pH of the solution, prior to entering the aquarium.

References

Reefkeeping.com article on calcium reactors
{{Aquarium Fishkeeping Aquariums

See also

References