Two weeks is a really long time on a res, esp in early flower.
Doubly so @ 1/2 strength.

I've pushed the PBP way up over 2k through stretch- some loved it ( pp), some less happy (blueberry).

Takes a couple runs to get it dialed in- well advised to underfeed ( reduced yeild) rather than overfeed ( cataclysmic die-off)

I think yer seeing underfeed, but I would be double-checking my pH with at least one differant meter/test before I ruled it out. Meters ( esp cheap ones- not too imply that your's is) can lie.