Just so you know, I calculate -0.3 for the saturation index when using a pH of 7.0, TA of 100, CH of 400 and Temp of 85F and that should be the same as your Taylor watergram if you use an "adjusted" TA of around 90 though that doesn't make a big difference. You might try target a somewhat higher pH, but don't need to go to 7.5 -- 7.2 is fine. A pH away from 7.5 is more of a concern for stinging of the eyes. Also, when you get close to 6.8 or 7.0, then depending on your pH test kit you might not be able to properly measure that low -- anything lower than the lowest on the test kit will look the same.

Richard