Wayyyyyyy to heavy....cut back to half...maybe even 1/4 for bit, see how they react.
More light, more nutrient use, the less light, less nutrients needed.
You are locking out probably.
FF
Need some info op...Temps, medium, auto/photo, etc.
First glance, lights are too low...frying them.
You need to slowly acclimate them to their new environment.
Lights high, then gradually lower to the sweetspot.
FF
There should be no fade at week 5...it appears to be either magnesium...burned tips as well as along the leaf edges...or potassium...hints of purple.
Watch new growth, your hypothesis sounds good, previous lockout from ph issues that may be fixed now.
Good luck.
FF
6.5 is locked into most growers' minds...I find it best to vary the ph slightly , always the higher side...6.8,.9 or even 7. Allows a drift as the medium dries.
I'm in soil though.
As stated above, mixing medium styles is tough.
Good luck.
FF
That looks like the beginning of a magnesium lockout...no additives or bs for a bit...good all around nutrient feed at a lower dose until she kicks out of it.
Happy grows.
FF
This and others were grown from seeds that came from a stressed MK plant...I have grown many, no problems.
These are my current run...i have run the seeds for nearly two years...not clones, from seed every run.
Peace.
FF