hey there, this is a magnesium issue, maybe even lock out : i see you're using epsom + cal mag, this is fine but the "low-ish pH" means the calcium + magnesium isnt getting chelated quick enough for absorbtion, dont change your pH though ! what you want to do is make a foliar spray with calimagic 3ml/L spray before lights on 3 times a week the problem should stop spreading and the plant will recover withing 14 days. Hope this helps ! 🚀