I keep a CO2 monitor next to the tank, and installed a whole home dehumidifier with fresh air intake to ensure that issue doesnt occur. #reef-fiend. Since its so easy to monitor pH its actually a really accurate, strong, real-time indicator for me. Skimmer getting some gunk on it gets addressed alot sooner too... o2 is entirely unrelated to pH btw.Ehh....that will work sometimes but ph has way too many factors involved beyond alk to consider that consistently correct. I.e. fresh o2 vs co2..is the skimmer producing less bubbles because it's dirty, are there more people in the house, is a window open, what's the season..blah blah
Alk, co2, temp, salinity = pH.