Yeah ph is perfect 6.0 yesterday 6.1 this morning. I use mad farmer ph adjustment. It's the best I've found for hydro. I was right there with you thinking that it must be iron zinc or magnesium, so three days ago when I did the res change I upped my cal-mag and flora micro. Definitely saw an increase in green and they have started to fill out much more but the same light growth nodes appear at new growth spots and the leaves look almost light bleached. I have a lumens reader and have the light casting about 65,000 lumens in the center and 35,000 on the edges of its footprint, still well within regulation. I'm stumped.... here's a picture of before the nutrient adjustment and after adjustment of the table.