Ok, let me clear what my confusion is. :spin2: Please correct me if I am wrong.
My knowledge of CO2, based on my planted tank. CO2 tank comes with regulator, solenoid, pH meter, Bubble counter, Needle valve, etc. The pH meter will let the solenoid knows whether the pH is too high or too low. This will trigger the solenoid to shut off.
Now, the calcium reactor. Basically you run the CO2 via the reactor by adjusting the bubbles from the CO2 tank. If the pH is too high or too low, then it will shut off the solenoid, hence there is no CO2 coming in the reactor.
Now, the APEX does the same thing. It will monitor the pH using the probe. If the pH is too high, or too low, it will shut off whatever that's affecting pH.
What's confusing me is that I have seen people have the pH probe in both the tank and in the calcium reactor. :uhoh3: It does make sense that you need it, in the tank. But the new reactor actually comes with the slot for pH probe as if it's needed to be in there.