Is this nutrient burn or lock out?

[drewparm]

I am brand new to this whole grow tent world. I have a few plants that are forming a pink/purple stem and forming some type of burns or deficiency on the same fan leafs. It isn't affecting the whole plant really. Just a few stems and leafs. I've been using Fox Farm Big Bloom and Grow Big the rec. Dosage per gallon once per week. Then watering in between. The general growth of the plants has been good with healthy looking leafs for the most part. I need some guidance.

 

[TripsRabbit]

I'd sprinkle a handful of garden gypsum on the soil b4 next watering if it were mine.

 

[GNick55]

are you letting it dry out before watering, looks like a bit of overwatering..
but you have to post pictures in a clear light!