What's Happening With My Leaves

[N420]

I noticed this on one of my plants I am day 25 of flower these spots are at the top leaves of the plant it's only effecting one of my 4 plants seems to have the slowest bud development I think it might be cal mag deficiency but not totally sure if it is cal mag is it as simple as adding cal mag to my nutes or should I flush the plant then add nutes with cal mag included any help would be greatly appreciated

light : 315 cmh
4x4 tent
temps 75-80
RH 40-45 %
medium: promix
nutes: seni bloom
bud candy
big bud
b 52

 

[Bigjake8]

Check for bugs pull a leaf off and scope it well next thing I believe would be P def but your running advanced so I'm betting on something eating on them