I only recently started using pH strips to test my F1, and I don't really see a point in it to be honest. First of all, it seems like the results are always the same! They are always around 3.0 pH, I even used different strips. I have tried testing right after I put in fresh sweet tea but don't remember the results, but it seems that after a few days, 1 week, and even 2 weeks, the results are always the same. Same for testing after F2. So I always just go by the taste of it.