Its starting on new growth and I'm about to switch them to flower, they started yellowing probably 2 weeks ago. I have just recently started using pH adjusted water, before it was at 9 now I use 6.5 pH. Grown in soil, temps are fine. Sent from my Pixel 2 XL using Grasscity Forum mobile app
avoid flipping until this issue is sorted the good news is the issue is on old leaves that suggests most of the nute burn is over ...you hope I'd flush pour 3 times the pot volume with ph'ed air temp water thru ther pot will reduce remove any excess heavy salts last wash add calmag and no more Feeding days end is good to recover over night good luck
With the ph being 9 the spots could have been anything. Extreme ph causes all kinds of nutrient lockouts. Like vostok said, flush em and then get back to a regular feeding schedule next watering.