HELP! Brown spots yellowing leaves

[Diesel200034]

Hi I’m a beginner at this and my girls are 2 week flower 4 strains soil grow with fox farm trio for nutes . I’m showing some yellowing leaves at top with some brown spots . They are lollipopped but lower growth isn’t that affected I’m trying catch this early to fix . I feed1 a week every other day water ph 6.5 thought was cal mag issue so yesterday I gave 1 tsp per gallon cal mag along with recharge and ph water . Today few more leaves yellow and purple stems on 1 plant other 3 seem ok . Any help would be appreciated I don’t know if it phosphorus but I’m doing 400 ppm feeding 1 week and my run off is about same right around 4

[Going2fast]

Leaning towards cal mag as long as your pH is around 6.5. the damaged leaves will not recover.