This process is slower than watching paint dry so do not expect quick changes. Hee hee hee! ;o) No need to test weekly; might be way expensive to do that. I do it monthly or every two months.
Obviously, to measure changes in blooms (meaning the shade of blue or purple or pink), you may need to do something like I do which is to take pictures of the blooms every year in order to compare. I only do this to one shrub which blooms in Spring and late in the Fall so I get pics twice a year -hopefully- using the same camera and I try to take the pics under the same conditions (8am and sunny). While not perfect, it makes it easy to compare from one month to another or year to year.
Q