What a minefield this growing malarkey is!! Took me a while to figure the problem. Thought i'd fixed my nutrient deficiency last week. Things got a little worse. I've checked the ppm of my run off and it was around 220 ( checkedph run off as well, was 6.2. Gave them a good feed tonight so hopefully all will be well.
You need to get a pocket microscope from amazon and check the trichome heads.
You're looking for ~85-90% cloudy trichomes, the rest can be clear (too young) or amber (too old, CBN)