It will have to be run separate. You could however use the Ph probe with the Apex as they are compatible however you would likely need to recalibrate it. The ORP probe port can be configured to be used as a 2nd Ph probe port for you Ca reactor. This assuming you're not using ORP.
That said, if you are using an ORP probe, I would suggest getting the PM1 and selling the AC3 to cover the costs. It's really better to manage from the Apex instead of using 2 parallel systems. Plus you will want to have the Co2 solenoid on a controlled outlet..