Deficiency or something else?

Week 3 veg
6-1000 watt MH
Rockwool mini cubes in grow flow 2.0- hydro
74f 37% humidity
Elite Gardens nutes with cal mag and hydroguard

Not sure what these leaves are telling me... roots look great. Ph has been on the swing since day 1. Moves from 5.8-7 in a day or two

I'm not a hydro grower but did you condition the rockwool before using them. They need to soak in an acidic solution before being used.

I always presoak the mini cubes for 24-48 hours in ph'd water but that is the extent of conditioning. Thinking the discoloration may be related it the ph swing?

See how all the tips looks small and lighter but the leaves around them are nice and lush? I'd say you ran out of magnesium. What do you think?

I think you answered your own question with the ph swing. If it's going to 7.0 you're locking out micros

http://www.growweedeasy.com/ph-fluctuations-cannabis

Adjust your ph further down, like to 5.4 or even a bit less, that way it will spend more time in the zone