Calcium Reactors Part 2: Assembly & Installation

This is the second video of a 3-video series dedicated to calcium reactors.

In Episode 1 of our 3-part series, we explored what is a calcium reactor, what is needed to run a reactor and what to look for when purchasing one for your system. Now that we have all components let dive right in and begin installation.

What is a calcium reactor?

Corals, invertebrates and even coralline algae are constantly using up calcium and alkalinity in our aquariums. A calcium reactor is a piece of equipment that helps simultaneously maintain alkalinity and calcium throughout the day attaining the ultimate in stability and growth of stony corals.

Reef Octopus offers a wide array of calcium reactors for aquariums ranging from a small 50-gallon system to large public aquariums in the thousands of gallons.  They come in single and double chamber and AC or variable speed DC recirculation pumps.

We will be assembling the Reef Octopus CR140 calcium reactor but all other models assemble the same way.

Reef Octopus Calcium reactors come disassembled for shipping. Assembly is rather simple and will only take a few minutes. Before we start, let’s make sure that all components are included and nothing is missing from the box.

Your Reactor Should Have

  • Reactor body with sponges and bracket
  • Plumbing
  • Recirculation pump
  • Probe holder
  • O-ring Seals
  • Tubing with check valve and shut off valves

Let’s begin assembly by placing the reactor and its included components on a flat, stable working surface.

Preinstalled O-ring on the recirculation pumps output

With the preinstalled O-ring on the recirculation pumps output in place, install the recirculation pump to the reactor body by threading the nut on the reactor counter clockwise. Be sure not to over tighten.

Silicone Grease will help preserve orings and enhance the seal

As with all O-rings I suggest you use food grade silicone O-ring lubricant to preserve the O-ring seals.

Grab the clear O-ring seal and insert it into the nut on the Intake Tee fitting and thread clockwise onto the intake threads of the recirculation pump.

Install one of the two black O-rings into the designated channel on the top union of the Tee fitting.

Place the second black O-ring within the plumbing near the top of the reactor.


Align the cross section plumbing to the Intake tee and to the connection coming from the side of the reactor. Turn the union nuts clockwise to lock and seal. Be careful not to over tighten.

Rotate the lid counter clockwise to remove.

Carefully insert the larger clear O-ring in to the channel around the lid.

The lid of the reactor has three ports: Effluent output, CO2 recirculation line and pH probe holder.

Thread the pH probe holder into the top of the reactor lid.

The probe plug should remain in place until a pH probe is ready to be installed.

The probe holder has a preinstalled O-ring to form a seal and a probe plug for when a probe is not in use. 


With a section of included tubing and a shut off valve we will create our CO2 recirculation loop to prevent the accumulation of gas at the top of the reactor chamber.


Attach one end of the line into the port opposite to the Bubble counter, then the other end into the port on the lid that does not have the extension tube on the underside.


With a tube cutter or sharp pair of scissors, make a cut in the CO2 recirculation line near the top of the reactor and install the valve by mending the line we just cut.


Now that the reactor is assembled lets carefully move it to a level and stable surface as close to your sump as possible. The shorter the hoses the better.


DO NOT LIFT the reactor by the flange or plumbing and NEVER EVER lift the reactor when it is full of water.

The Reef Octopus reactor recirculation pump can be submerged in water and can be installed in a sump if desired.

Lets begin the CO2 Installation

With the CO2 cylinders main valve off, Attach the dual gauge regulator and tighten securely using a Teflon gasket. DO NOT use any paste or tape.

The gauge on the left reads CO2 levels in the cylinder

The gauge to the right reads the pressure of the gas leaving the regulator.

Attach a length of supplied tubing to the regulator and then to the bubble counter on the reactor.

Cut the tubing close to the bubble counter and install the CO2 check valve with the arrow pointing towards the bubble counter.

Close the needle valve on the regulator.

Slowly open the main cylinder valve and dial in the adjustment knob on the regulator until the outlet pressure gauge reads 3-5 psi.

Do not connect your regulator to power at this time.

Connect a short piece of the included tubing into the reactor’s intake located at the bottom tee that is aligned with the intake of the recirculation pump.

Attach a valve and then another length of tubing that connects to your water feed source.

As we covered in our previous video, there are three possible methods to feed the reactor:

  • Gravity (which we do not recommend)
  • The second and most used method is by pushing water through the reactor with a small feed pump and regulate the flow using a small pin valve on the reactor’s output also known as the Effluent. It is critical that we use a small pump as we are only looking to feed enough pressure to match the pressure from the CO2 inlet and the effluent. Problems arise when one is higher than the others.
  • The third and recommended option is a peristaltic pump like the Kamoer FX-STP connected to the reactor’s output (not input) and pull water through the reactor and back into the sump. It provides the very best in stability, control and accuracy. The FX-STP will provide continuous flow that can be adjusted between 0 and 150 ml/min.

In this video, we will opt for the third option.   

Place a line in the sump and secure it in place below the water surface but away from the bottom and connect the other end to a valve.  Using a short piece of line, connect the valve to the reactor’s intake. 

Using a barbed adapter that can be found at your local hardware store, connect the flexible tubing included with your Kamoer pump to the reactor’s output located on the lid. Connect the other end of the line to your Kamoer’s input. 

Now attach a line to the pump’s output and secure the other end of the line in the sump above the water level. 

Remove the reactor lid, retainer bracket and top sponge.  With one sponge in place at the bottom of the reactor, carefully fill the chamber ¾ of the way with rinsed calcium carbonate media.  Place the top sponge on top of the media and then the retainer bracket (table side down) on top of the sponge.



Now, close the valve located on the reactor’s intake and fill the reactor chamber to the rim with tank water.  Screw on the lid making sure that the O-ring is properly installed. 

At this time we can install the pH probe into the holder to monitor and control the CO2 level inside the reactor.

As with any probe, be sure to properly calibrate it using the instructions provided by your controller. For calcium reactors, it is common to calibrate the probe to the low range using pH4 and pH7 calibration solutions.

Unscrew the nut from the probe holder and remove the plug from the center. Take the O-ring off plug.  

Slip the nut on the pH probe and then install the O-ring sliding it about 3 inches from the bottom tip.

Insert the probe with nut into the holder on the lid and tighten then nut to secure the probe in place.

Now it is time to start the reactor. 

First, connect the recirculation pump to power and run it at full speed. 

Second, open the valve located on the reactor’s intake line. 

Finally, start your Kamoer pump.  We recommend running the pump at about 50ml/min or higher for at least 2 hours to ensure all trapped air is purged from the reactor.

After purging the reactor reduce the speed of the Kamoer FX-STP to 20-30ml per minute. Now connect the CO2 regulator to power or a controller if you are using one. 

Adjust the needle valve to obtain a bubble count of about one bubble every 3 seconds. Remember that when adjusting the bubble count, there is a lag time since the hose has to accept any changes in pressure.

Monitor the reactor closely until the pH inside reaches 6.6-7.  This is a good time to set your controller to automatically shut off the CO2 regulator if the pH level inside the reactor goes below 6.6.

Now we have a fully running calcium reactor that is ready to be dialed in.  As always, inspect the reactor for leaks before leaving it unattended. 

In the next episode, we will discuss how to fine-tune a calcium reactor to your system’s needs. We will cover what to test for and what to do when our Alkalinity and Calcium are out of whack.  We will also go over some commonly asked questions and troubleshooting.  Our goal is to help reefers like you maintain successful reef tanks by providing you with the key information that will make a calcium reactor easy to understand and use.

If you have any questions or issues with the product, don’t hesitate to visit our support portal at Our friendly support reps are eager to help you with any questions or issues you may have. 

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Author: Carlos

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