Hey chef, I suggest to inspect Herschel and the others plants, it isn't Cal/Mag deficiency, it seriously look like spider mites bites.
Check all the others leaves, the first leave infected is a kind of first base where they eat and reproduce then the colony moves and females start to let their eggs a lil bit everywhere.
This leave is the first sign of an invasion, and the first wave looks to be massive as your leave have been bitten on the 5 fans on all the veins from the petiole to the tip.
I seriously hope I'm wrong ..... but start your full inspection, if I'm right I suggest you Sierra Natural Science SNS 217.
@WeedishChef,alright, by the spectrum I wasn't sure if it was MH or CMH.
These plants are 100% healthy, not even 1 tips burn, no purpling stems, they're perfect π
@Bigpun, Thanks Bigpun. I almost messed this grow up because of my misdiagnosed bug problem. They all recovered nicely though. I'll be posting harvest pics shortly.