I've noticed that during veg my ph moves naturally up as the plant consumes nutrients and lets out waste. In flower it's reverse and my Ph goes down. With Jack's I normally balance mine twice a day, morning and night. When the PH stops fluctuating to me it's the plant signaling that there isn't anything left to eat, and it's time for a res swap, or to add more nutrients.
I've heard other lines don't swing as much, but Jack's just works and it takes me about two minutes to balance my five-gallon bucket. I also don't run a chiller my res temps are 74-80, I never get root rot.