The only probes that aquacontrollers are compatible with are pH, ORP, DO, Specific Conductivity and salinity (temp also). Aqueous CO2 sensors are uncommon, especially at a small scale. However, if you control your input source water's alkalinity, you can have a pretty good approximation of CO2 content via pH and temperature. Here's a little light reading:
https://srac.tamu.edu/index.cfm/event/getFactSheet/whichfactsheet/112/
How precise do you need the CO2 readings to be? I would think that using the pH/Alk/temp relationship that you can get a decent idea of your CO2 concentration. As for being able to monitor this real time via the APEX, youre SOL. You would probably need to construct a project specific SCADA type of system, and youre talking big bucks now.