Calcium Reactor Theory and Setup

Calcium Reactors are excellent systems designed to add a steady amount of natural elemental calcium and minerals to a marine aquarium system.
This is achieved by the careful addition of CO2 gas to the system seawater, thus lowering its pH to the acidic range and passing this seawater through aragonite coral chips housed inside the reactor (see diagram).

Because the CO2 treated seawater has a pH in the range of 6.6 – 6.8 (or lower); it will readily dissolve aragonite coral chips housed inside the calcium reactor. This enriched calcium seawater, also called effluent, should be sufficiently aerated to drive off the CO2 and return the pH to the normal range while still carrying the additional calcium in solution before it is re-introduced back into the aquarium.

You will be controlling the pH of the fluid inside the reactor. Generally speaking a pH of 6.6 – 6.8 (or lower) will readily dissolve aragonite media. If the pH of the seawater surrounding the aragonite is too low, the aragonite will turn to “mush” and no longer have fluid flow through the chips. If the pH is too high there will not be a sufficient acid environment to dissolve the aragonite. Trial and error with your brand of aragonite should be performed.

***Note: Properly designed Calcium Reactor Systems will add natural elemental calcium and minerals to your system and will have virtually no effect on the pH of the aquarium.

There are several equipment considerations:

  • Calcium Reactor
  • Aragonite Media
  • CO2 Tank
  • Electric CO2 Solenoid
  • PINPOINT® pH Controller

Consider the following setup into a marine aquarium sump:

Calcium Reactor – houses the aragonite chips and has a mechanism to infuse CO2 gas inside the reactor. Some models have a built-in port to accommodate a pH probe. Many reactors do not have a port. Models without a port should have the output water (effluent) exit the reactor and collect in a small cup located in the sump area (see diagram). The probe of the pH Controller should be installed in the collection cup so as to measure the pH of the seawater from the Calcium Reactor. As this collection cup fills, it will overflow into sump where it should be properly aerated to drive off the CO2 and return the pH back to normal seawater levels before it enters the aquarium. An airstone or aerating powerhead in the sump area can be beneficial.

CO2 Tank or Bottle – This will be your source of CO2 gas. Obviously CO2 gas when mixed with seawater will lower the pH of seawater. CO2 bottles are easily, and inexpensively, refilled at any welding supply store or any outlet that will recharge fire extinguishers.

Electric CO2 Solenoid – An electrically activated valve that when energized by the outlet on the back of the PINPOINT® pH Controller, will allow CO2 gas to exit the CO2 bottle to be released in the aragonite of the Calcium Reactor. This CO2 gas will quickly lower the pH of the seawater inside the reactor. A bubble counter, if available, will visually indicate the volume of CO2 exiting the bottle. This gas volume can be adjusted via the needle valve on the solenoid.

Aragonite – Basically coral fragment. You should experiment to find the pH levels that will dissolve the aragonite most efficiently. If the pH is too low the aragonite will turn to “mush” and no longer have flow through it. If the pH is too high then the aragonite will not be dissolved sufficiently.

PINPOINT® pH Controller – The electronic pH measurement and control device that will activate the CO2 solenoid to start or stop the CO2 gas flow to the reactor.
Not all pH Controllers can control devices that will influence pH in both an increasing and a decreasing pH direction as needed. The PINPOINT® pH Controller is perfectly suited for any calcium reactor application by controlling pH downward during CO2 addition. It will also control pH upward by using a regular air pump to drive off the CO2 from seawater.
Typical setpoints would be to begin the CO2 flow at a pH of 6.8 and stop the CO2 flow when the pH of 6.6 is reached.

The PINPOINT® pH Controller will:
– automate the proper pH settings inside the calcium reactor
– save CO2 by using it only when necessary
– save aragonite by keeping the pH levels in the proper range
– allow easier adjustment of flow through the reactor by keeping pH in the proper range through a range of different fluid flow and CO2 volumes

To optimize reactor efficiency experiment with:
– lower pH settings to dissolve more aragonite
– Increased CO2 flow to the reactor
– decrease (or increase) the water flow through the reactor
– install an aerating powerhead in the sump to drive out the CO2 gas and return the effluent to normal seawater pH levels before returning to the aquarium.

Some hobbyists want to place the pH electrode directly into the aquarium water. Their objective is to use the pH controller as a safety device to shut off the CO2 gas in the event the aquarium pH becomes too low because the effluent containing the CO2 is being introduced back to the aquarium water at too fast a rate and/or without proper aeration.

  • Pros
    – You can use the PINPOINT® pH Controller to monitor the pH of your aquarium
  • Cons
    – CO2 gas will be infused constantly whether it is actually needed or not
    – You will not be able to monitor the pH of the seawater inside the reactor.
    – Flow rate and CO2 input to the reactor will be more difficult to adjust and therefore the reactor pH will more easily be "out of optimal range" frequently too high or too low.