I'm usually around 5.9-6.0 running jacks and very low ec tap water. Always hits that figure when I mix a new res. I don't mess with it because its within range. I've grown in coco as low as 5.6-6.0 without any issues.
5.7 - 5.9 Veg
5.9 - 6.3 Flower
Beat practice to let your ph move through the ranges so that no one element is ever locked out or only available for a smaller window than what you achieve by letting it naturally move through its available range.