Ph looks super low.
Calcium and more importantly alk appear to be very unstable.
Those two things alone will cause what you are seeing here...
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Ph looks super low.
Here is my ph reading, i got the ph buffer not sure if i dos itOn your APEX charts:
1) pH of 7.63. Probably not calibrated, but that would hurt corals.
2) A temperature swing of 5 degrees
3) Got nitrates?
My guess is your CaRx may be dumping CO2 into the effluent or leaking CO2 gas into the sump cabinet and the skimmer is injecting it into the the water. Check your chart history on pH. Keep looking backward for at least 4 weeks. Anything change?