Have you tried outside air to the skimmer?I ran a calcium reactor for nearly 10 years and actually just switched back to dosing. The reactor generally had no issues keeping pace with demand but I could never get the pH in my reef high enough. Tried several things but since the tank and sump are in the basement I'm already at a disadvantage. Tank is now running with GHL and director/dosing pumps. I really do like the CARX method quite a bit but made the switch and I'll see how it plays out.
2nd chamber to drive off co2?
I have a my sump and ph today is 8.2