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Calcium Reactors


A Calcium Reactor consists of a column made of acrylic or PVC which varies in length and width depending on the size of the system. This column is filled with media such as gravel limestone coral. Water from the aquarium is circulated through the gravel using a dedicated pump. Because of the fact that calcium carbonate does not dissolve at pH prevailing in the main tank of the aquarium, it is necessary to produce a low pH inside the reactor chamber by the administration of carbon dioxide.

Dosing CO2 acidifies the water to between 6.0 - 6.5 pH. As a result, the media limestone slowly dissolve releasing calcium carbonate and other minerals and elements that are contained in the particular media. Since in most of the media content 99% is usually calcium carbonate, addition of other elements is limited. Water flowing out from the reactor is rich in calcium and carbonates but the pH is low. Tuning rate of the stream from the reactor and / or the amount of CO2 flowing into the reactor determine the pH in the reactor itself, and hence the levels of calcium and alkalinity, which are present in the eluate.


Modern calcium reactors differ in the direction of water flow, fluidization or lack of it in the media, the method for introducing CO2, the amount used in the chambers and the way they cope with the excess CO2.

Aqua Special Calcium Reactor The new generation Aqua Special reactors have been designed using the "upflow" reverse flow method, where water rises from the bottom of the chamber, which prevents the entrapment of any debris and excess accumulation of organic matter.

Thanks to implementation of a very quiet and efficient pump from the Silent Jet series we achieved a very efficient flow through the media of water and CO2, hence faster dissolution of calcium carbonate.

One of the distinguishing characteristics of our reactor is the fact that the dosed carbon dioxide is used in 99%, which means that the accumulated CO2 in the upper chamber flows back into the circulation and this process continues until completely dissolved.

Our system results in:
  • less frequent dosing of CO2
  • extremely high performance of the reactor
  • much faster medium dissolution
  • less carbon dioxide finds its way into the tank
  • summary pH of the eluate received by the tank is higher
All KM series reactors are equipped with ball valves for optimal control of the water flow.
They are built so that the cartridge can be replaced quickly and easily, and the innovative latch provides a very good seal, even at high pressure.

In most projects, the bubble counter chamber contains fresh water. The water eventually evaporates, and the chamber requires constant filling. To prevent this from happening, Aqua Special introduced the bubble flow meter which does not require servicing thanks to the water flowing through the reactor. This project ensures that the chamber introducing CO2 to the water is always filled and the bubbles can always be seen climbing to the top.

The corresponding rate of flow of CO2 bubbles and the eluate is key to ensuring optimum levels of calcium and alkalinity. Aquariums with low levels of calcium and alkalinity demand more saturated effluent until appropriate levels are achieved. A similar situation occurs when more corals are introduced to the tank, and they are expanding, the demand for calcium and alkalinity increases, which forces to re-tune the reactor.

It is impossible to give precise instructions for the best flow rate, because each tank varies in size and has different requirements for calcium and alkalinity. The aquarist should monitor the pH, the eluate, calcium and alkalinity in order to determine the best combination of speed of introducing the CO2, and the rate of return of water to the aquarium. However, it is advised that during the initial installation the calcium reactor, to set it to a low rate of CO2 dosing. This allows for a slow increase alkalinity and prevents coral bleaching. Low alkalinity in the tank may indicate that the addition of large amounts of CO2 into the water resulted in a significant decrease in pH, which will affect the health of the inhabitants of the tank. Once you get a slow increase in the levels of alkalinity to acceptable ranges, the pace of CO2 can be increased if necessary.


Typically, the CO2 is routinely supplied to the reactor through needle valve to adjust the pace of implementation. When the rate of bubbles is already set, it maintains the rate of entry of CO2, but nevertheless requires constant observation of the effluent pH to ensure that an adequate level for the dissolution medium is maintained. In addition, when the media is soluble, less CO2 will react with what is left in a reactor. In systems that use a fixed input of CO2, can be observed that the greater amount of carbon dioxide goes into the aquarium, lowering the pH of the system. Excess carbon dioxide can also accumulate inside the chamber creating a vacuum at the top, which can lead to plugging of the pump.

An alternative is to use a pH probe and a dosing controller of CO2. In this case, the pH of the water in the reactor is controlled at all time. If the pH rises above a fixed point, CO2 is dispensed and in effect lowers the pH back to the desired level by closing the solenoid valve. This helps to reduce the use of CO2, and ensures that the reactor maintains constant pH levels. In order to be secure, make sure that the CO2 solenoid valve is designed in such a way that it shuts off when there is no power. This ensures that CO2 will not be shipped to the reactor if there is a power outage, otherwise, the pH of the reactor could fall to very low level, and acidic water could badly affect the aquarium. Also, the pH probe must be regularly calibrated to always give the correct readings of the pH reactor.

Aqua Special Calcium Reactor
The media types which are used in calcium reactors are a topic of discussion for a long time. The main aspects are the cost, the rate of dissolution and phosphate content. Some of the media which can be used depending on the type of reactor, include oolitic sand, hole saw shell, coral gravel, coral algae marl, crushed limestone, marble petals and layers of limestone. Some media sources are released when the phosphate is dissolved. This can result in significant amounts of phosphate, which is added to the aquarium in a certain period of time. If the aquarist does not know the reactor effluent phosphate levels, it can be measured using the AquaSpec computer. If the phosphate was found, the medium can still be used if the reactor effluent passes through the adsorbing phosphate media (ie, granular iron-based media) before it enters the aquarium. You can also pass the effluent through a filter or refugium algae, where macro algae to absorb excess phosphate and CO2. In addition, stimulation of growth by these nutrients would also help in removing nitrate from water. Overall, calcium reactor media created with the form of aragonite calcium carbonate are among the more preferred the form of calcite as the pH level required for its dissolution may not be as low as for calcite.


In small reactors, small media (2 - 4 mm in diameter) can be used without major problems. However, as the height of the reactor increases, small media clog up easily with tiny flecks and are lifted up by a recirculating pump as a single mass. In this case, bigger media (1 - 2 cm) should be used, so the water can flow through.

Aqua Special Calcium Reactor CALCIUM

Calcium concentration in natural seawater is about 400 mg / L. In areas near coral reefs, sea water has a tendency to slightly increase the level of calcium from about 420 to as high as 480 mg / L. It simply means that the aquarist should seek to maintain the level of calcium in the reef aquarium to a close of 400 mg / L at a specific gravity of 1.025 at. Comparisons of measurements of calcium ion concentration in seawater must include the level of salinity (or specific gravity), because the calcium concentration increases with increasing salinity, and vice versa.


Alkalinity is a general term that includes the number of compounds, which together allow water to buffer the effect of lowering the pH of the acid (hydrogen ions, H +). These compounds contain bicarbonate, carbonate, boron, silicate, hydroxide, and even phosphate. Taken together, these compounds represent the total alkalinity of seawater. Despite the fact that other compounds contribute to the alkalinity of sea water, bicarbonate and carbonate are the most important simply because bicarbonate accounts for 90% of the total alkalinity, and carbonate for 7%, total alkalinity of natural seawater is between 2.1 and 2.5 meq / L (6 - 7 dKH). In aquaria, which received a very small amount of alkalinity supplements, the values may be as low as 1.0 meq / L (2.8 dKH).


When you add calcium and alkalinity do not forget to add the same proportion as they are used in the manufacture of carbonate calcification. The precipitation of calcium carbonate uses its two components in the exact ratio of 1:1. This corresponds to one meq / L (2.8 dKH, the equivalent of 50 ppm CaCO3) for each 20 ppm of calcium.




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