__NOTOC__ 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 appropriatel ...

s, a calcium reactor creates a balance of

alkalinity Alkalinity (from ar, القلوي, al-qaly, lit=ashes of the saltwort) is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength ...

. An acidic solution is produced by injecting

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

into a chamber with

salt water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish wat ...

and

calcium Calcium is a chemical element with the 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 t ...

rich media. The carbon dioxide lowers the pH by producing a solution high in carbonic acid, and dissolves calcium. The effluent is returned to the

where the calcium is consumed by organisms, primarily

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

s when building skeletons. A calcium reactor is an efficient method to supply calcium to a reef aquarium. Reactors may be used in elaborate freshwater and brackish aquariums where freshwater clams and other

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...

need a constant supply of

. 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, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

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

(CO₂) in order to create carbonic acid (H₂CO₃). This increases the solubility of the calcium carbonate. The reaction frees the calcium and carbonate, supplying the aquarium with water rich in Ca²⁺ and CO₃²⁻, important for maintaining alkalinity and calcium levels. The bubble counter measures carbon dioxide. 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 threaded, needle-shaped plunger. It allows precise regulation of flow, although it is generally only capable of relatively low flow rates. Construction and operation An instrument ne ...

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 ty ...

regulates the CO₂ bubble rate. Valves with precise adjustment abilities improve bubble control. The feed pump controls the volume of water exchange. This is important because a high rate of water flow into the reactor reduces 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 Back pressure (or backpressure) is a resistance or force opposing the desired flow of fluid through pipes, leading to friction loss and pressure drop. The term ''back pressure'' is a misnomer, as pressure is a scalar quantity, so it has a magnit ...

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 pumps are effective operating against pressure, capable of supplying an adjustable and continuous flow over flow rates with minimal maintenance. The pH control is connected to a probe in the reactor and adjusts the rate at which the calcium media dissolves. This probe monitors the pH level in the calcium 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 control closes the valve as the pH falls below this level. 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.

References

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

See also

References