The overlapped leaves look like hplvd, but they are definitely starving. Phosphorus deficiency turns them purple and whole leaf yellowing is nitrogen et.c. Also when it's cold she'll uptake more phosphorus. Those fall colors are from using all the nutrients and not what you want to see for a few...
Nice looking lady! So in a constant feed system, such as coco or hydro, magnesium is in constant demand. Sounds like they got over watered, over nuted, and cal mag deficient. Let it dry then water her with 2000ml ro water with 5 ml slf-100 and 2ml flawless finish (or Epsom salt with no additives...
Agreed, they sell a meter that measures ppm, ec and ph for less than $40 on amazon. Just keep the ph calibrated, tested often and use slf-100 when salts build up. Flawless finish if you burn them.