pH & Water Surface Tension
Spa Marvel reduces the surface tension of the water. When surface tension is reduced, pH will naturally rise a little bit. pH that is high due to the natural rise will not cause cloudy water, reduced sanitizer efficiency, scaling, odours, bather discomfort, or anything untoward as it can in traditional (non-Spa Marvel) water care.
When using Spa Marvel as long as pH is between 7.2-8.4 it is in an acceptable range. If you try to lower pH to the ranges that are recommended in traditional spa water care, it will cause the alkalinity to drop, and while the pH may drop for a period of time, it will tend to creep back up. So, as long as your alkalinity is between 80-150 (where 120-150 is ideal), if the pH is a little higher than what you are used to, leave it alone.
Amusing Surface Tension Experiment: https://youtu.be/2F64qh9qPAI