Is this pH related?

I think you're looking at a phosphorus deficiency here... and that is a direct result of the soil being too acidic - i.e., your pH is out of whack. Just because they have the words "pH Perfect" in their name doesn't mean that you can ignore the pH and never check it... doesn't work like that! I would give this gal a good flush with 3x the pot volume of pH'd water and make sure the water is pH'd to between 6.0 and 6.4... 6.2 or 6.3 is preferable... add 1/2 strength nutes to the last gallon of water you run through her... going forward, always check the pH of anything you give her be it plain water or a nute solution... if you don't have one, I would strongly recommend investing in a pH pen (I use Apera but Blue Lab seems to be the "gold standard") .... making sure the pH is correct will avoid a LOT of problems in any grow... Good luck!