pH=potential Hydrogen
Airating the water will increase the potential Hydrogen in the water resulting in higher pH in the water. I do not beleive air has a high pH, it is the introduction of the air to the water that results in the pH increase.
The more jets you have in your spa, the more pH creep you will experience. The same can be said if the spa is used more.
SpaGuard lists this on its weekly maintenance printouts:
2.
Test and adjust pH regularly .......Spas with a large number of therapy jets (>
tend to experience high pH
HTM