Calcium reactor
Encyclopedia
In marine
and reef aquarium
s, 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
by producing a solution high in carbonic acid
, and dissolving
the calcium media. The effluent is then returned to the reef aquarium
where the calcium is consumed by organisms, primarily coral
s when building skeletons. A calcium reactor is one of the most efficient methods of supplying calcium to a reef aquarium. Although more commonly used with marine reef aquariums, calcium reactors are beginning to find use in elaborate freshwater
and brackish aquariums where some species of freshwater clams, corals, and other invertebrates may need a constant supply of calcium
.
CaCO3 + H2O + CO2 <——> Ca2+ + 2HCO3-
), 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 frees the calcium and carbonate, supplying the aquarium with water rich in Ca2+ and CO32-, important for maintaining both alkalinity and calcium levels.
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
or solenoid valve
is used to regulate the CO2 bubble rate. Valves with precise adjustment abilities will improve bubble control characteristics.
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 pump
s are effective operating against pressure, capable of supplying a precisely adjustable and continuous flow over a variety of flow rates with minimal maintenance.
Many pH controllers also incorporate an interface for an air pump. This air pump is usually connected to an airstone located within the sump or main tank. If the probe detects a pH level below the set range, the pump will activate and the resulting bubbles raise the pH by helping to dissipate the CO2 gas.
Marine aquarium
A marine aquarium is an aquarium that keeps marine plants and animals in a contained environment. Marine aquaria are further subdivided by hobbyists into fish only , fish only with live rock , and reef aquaria. Fish only tanks often showcase large or aggressive marine fish species and generally...
and reef aquarium
Reef aquarium
A reef aquarium or reef tank is an marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the coral reef environment...
s, a calcium reactor is a device used to create a balance of alkalinity
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
in the system. An acidic solution is produced by injecting carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
into a chamber with salt water
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
and calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
rich media. The carbon dioxide lowers the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
by producing a solution high in carbonic acid
Carbonic acid
Carbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
, and dissolving
Solvation
Solvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...
the calcium media. The effluent is then returned to the reef aquarium
Reef aquarium
A reef aquarium or reef tank is an marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the coral reef environment...
where the calcium is consumed by organisms, primarily coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
s when building skeletons. A calcium reactor is one of the most efficient methods of supplying calcium to a reef aquarium. Although more commonly used with marine reef aquariums, calcium reactors are beginning to find use in elaborate freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
and brackish aquariums where some species of freshwater clams, corals, and other invertebrates may need a constant supply of calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
.
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 7.8, so to reduce the pH carbon dioxide (CO2) is used. The general reaction formula is:CaCO3 + H2O + CO2 <——> Ca2+ + 2HCO3-
CO2 Chamber
Inside the reaction chamber, a calcium rich media (aragoniteAragonite
Aragonite is a carbonate mineral, one of the two common, naturally occurring, crystal forms of calcium carbonate, CaCO3...
), mainly CaCO3, is forced into contact with water injected with carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) in order to create carbonic acid
Carbonic acid
Carbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
(H2CO3). This increases the solubility of the calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
. The reaction frees the calcium and carbonate, supplying the aquarium with water rich in Ca2+ and CO32-, 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 rateVolumetric flow rate
The volumetric flow rate in fluid dynamics and hydrometry, is the volume of fluid which passes through a given surface per unit time...
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
Needle valve
A needle valve is a type of valve having 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 :...
or solenoid valve
Solenoid valve
A solenoid valve is an electromechanical valve for use with liquid or gas. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports...
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
Siphon
The word siphon is sometimes used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in the English language today, the word siphon usually refers to a tube in an inverted U shape which causes a liquid to flow uphill, above the surface of the reservoir,...
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
Back pressure refers to the resistance to a moving fluid by obstructions or tight bends in the confinement vessel along which it is moving, such as piping or air vents, against its direction of flow....
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 pump
Peristaltic pump
A peristaltic pump, or roller pump, is a type of positive displacement pump used for pumping a variety of fluids. The fluid is contained within a flexible tube fitted inside a circular pump casing . A rotor with a number of "rollers", "shoes" or "wipers" attached to the external circumference...
s 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. This probe constantly monitors the pH level within 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 also closes the valve as the pH falls below this level.Many pH controllers also incorporate an interface for an air pump. This air pump is usually connected to an airstone located within the sump or main tank. If the probe detects a pH level below the set range, the pump will activate and the resulting bubbles raise the pH by helping to dissipate the CO2 gas.