DIY: Calcium Reactor
One of the best ways to maintain alkalinity and calcium in the reef aquarium is the calcium reactor. The basic idea of the reactor is the reverse process of calcification. A calcium carbonate media is dissolved using carbonic acid (generated by addition of CO2 to water) to provide the Calcium and bicarbonate ions, in the same proportion that is used during calcification 
CaCO3 + H2O + CO2 <-> Ca2+ + 2HCO3-
So the calcium carbonate reactor is basically a device that brings the three ingredients together in a manner so as to allow efficient production of Ca and bicarbonate.
The DIY calcium reactor on the picture has been made in June 2004. Its stable and compact construction, the easy operation, the small footprint and the low price of parts have made it the good choice for DIY. The picture on the left represents calcium reactor filled to capacity with coral sand. Ca reactor 3 months later, when one third of coral sand is already dissolved, is shown on the right picture.
The basic part of my DIY calcium reactor is 12 cm (4.7")diameter and 40 cm (15.7") long tube, made of 5 mm (0.2") thick acrylic. Most of Ca reactor parts ,including pump are inside of this tube, so size of tube actually define also size of complete reactor. CO2 is taken up by an injector system. Bubbles of CO2 which have not been used are caught on the top of reactor and are injected into the reaction chamber again. In this way not a single bubble can leave the reactor without having been used.
This reactor( 12 cm diameter and 40 cm high) can be filled with up to 3000 grams of coral sand (2.3 liters). If necessary it is possible to dissolve up to 0.9 kg of coral sand per month by this Ca reactor.
The mixture of CO2 and H2O is continuously circulated in the chamber through the calcareous medium in a closed circulation loop. Water from the tank/sump enters the reactor through an inlet and exists through a outlet, both of which are connected to the chamber with calcareous medium.
The following schematic show all important parts of my DIY Ca reactor illustrated with different colors:
- 3.) Pipe connected to bouble counter, ...., C02 bottle.
- 4.) T part used for connecting injected CO2 and unused CO2 caught on the top of reactor .
- 5.) Pipe used for connection to MaxiJet 1000 pump inlet.
- 6.) Regulation valve used for setting the speed of unused CO2 dosing. If valve is closed unused CO2 dosing is also closed.
- 7.) ON-OFF valve, which is normally closed and it is opened only during initial filling of Ca reactor with water.
- 8.) Pipe inside reactor.
- 9.) Regulation valve used for setting of the water flow between sump and Ca reactor.
- 10.) Pipe outside reactor used for collecting water from Sump.
- 11.) Pipe inside reactor used for connection to MaxiJet 1000 pump inlet.
The MaxiJet 1000 pump is used for internal circulation of water inside reactor. My DIY reactor has a top to bottom circulation loop. Water flow through the coral sand downwards, from pump outlet on the top of the reactor to the bottom, where pump sucks water through 16 mm PVC pipe. This pipe is connected to the pump MaxiJet1000 inlet.
The internal recirculation rate is 1000 liters per hour, while typical input/output rates are in several liters/hr (depending on the settings). Water entering the reactor comes in at tank alkalinity and Ca levels and effluent leaving the reactor has much higher alkalinity and Ca. The amount of CO2 added is typically measured in bubbles/min. Unfortunately there is no standard bubble size, so this is a dubious measure when comparing different reactors.
CO2 injection system
The CO2 injection system is represented in the following picture. System consists of the:
Water flow between tank/sump and Ca reactor
Water from the tank/sump enters the reactor through an inlet and exists through a outlet, both of which are connected to the chamber with calcareous medium. Inlet system consists of pipe (10), which is connected to sump and pipe (11) inside reactor used for connection to MaxiJet 1000 pump inlet. See also picture 1. Outlet system consists of pipe inside reactor (8) , regulation valve (9) used for setting of the water flow between sump and Ca reactor and pipe connected to the sump.
There are a number of ways to supply the calcium reactor with water from the tank. The following methods are compatible with my DIY Ca reactor:
1.) Siphoning water into the suction side of the calcium
reactor's MaxiJet pump. Personally, I use use this method.
2.) Simple gravity method.
3.) Peristaltic pump to supply water to the reactor. According to my opinion, this the best method, but you will need peristaltic pump.
CO2 reinjection system
The bubbles of CO2 which have not been used are caught on the top of reactor and are injected into the reaction chamber again. The CO2 reinjection system consists of the:
The regulation valve (6) is used for controlling the reinjection of unused CO2. If regulation valve (6) is closed, reinjection of unused CO2 is stopped.
Huntington Simon, A Guide to Using Calcium Reactors
Sanjay Joshi,Calcium Carbonate Reactors
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