I realize that pH and temperature will vary, however in most cases they will vary by limited amounts on a daily or weekly basis. For example pH, if the pool is being maintained on a regular basis, then the pH will not wander outside of a very small range. After all that is why we test the water. Like wise the water temperature. This will vary seasonally, however on a daily basis, the range of temperatures will not be that great.
What I am getting at, knowing the water parameters, I choose a target pH that will set my CSI. I have an acid pump so typically my pH will not vary by more than 0.1 pH in a week. Each week when I have a new set of test results, I calculate a target pH that will give me my desired CSI.
In any case I am one of those people that have hard fill water so have high CH. I have been processing the water to lower the CH, which is working, and I have noticed that my target pH is also rising. At this point with a CSI of 0, my pH is at the upper end of the range.