Jeeeez guys! It needs Cal/MAG! I'm sure he's using RO water, and needs it!
Perhaps, I've seen a few trying to use only distilled water.
Come on! 6.3 PH won't wont do that Sticky. You know better than that.
Did you just water the plants, or has the plants been sitting in the moist soil for a few days? From what I can see looks like it is under/over watered depends on if you just watered them or it has been sitting in that soil wet that long. Needs slightly more N and add a bit of Mg. Other wise they look fine to me. Few tweaks is all it needs.
Edit: I am leaning towards adding some Mg or epsom salt
Sounds good, but also other possible issues. I may as well be told I should know better also.
Is he new or a vet with a never before encountered problem?
Does not say which promix, some are pre nuted. New clones, how well developed are the roots? Freshly transplanted, do they have sufficient soil contact? Freshly transplanted into pre nuted soil plus being fed? Freshly transplanted, moist soil or drenched?
Just a possibility I do not know anything about him so I can ask does he know when a clone has sufficient roots for planting?
Yellowing leaves on cuttings
When unrooted clones start to yellow it means they are either not touching the rooting medium good enough, to much co2. The vast majority of the time, an unrooted cutting will begin to yellow some of it's leaves, starting with it's largest oldest leaves, because it is too close to the lights and it needs to be moved farther away. Some yellowing is normal just as the cutting begins rooting and can be a sign of the cutting using it's oldest leaves as a food source while it is forming new roots. Plain tap water that is ph adjusted is just fine until the clones have rooted. Giving any ferts will kill them untill they have been rooted.
http://www.420magazine.com/forums/problems-pests-disease-control/81275-cannabis-plant-pest-problem-solver-pictorial.html Near Bottom of the page
When you feed someone enough possibilities they should be able to solve the problem by looking back at what they have done to get where they are.