as far as yellowing of more mature fan leaves... i had a sour candy that started looking yellow on the older fan leaves... i gave it a epsom salt boost and that helped some... but i found that the big problem was that i had a pH lockout issue. test that runoff pH if your running drain to waist. i tested my hempys and my pH was sky high. i flushed with some heavy acid water to get the pH where I wanted it and they did a lot better... i finally realized that basically what had happened to mine was the pH lockout caused the plant to start burning its own stock supplies. kinda like a clone does right after cut. if you notice that it may be pH issues or maybe just underfeeding. I also noticed that with strait 12 from seed in perlite i was able to run a full strength nute of GH flora series Lucas formula in drain to waste. My first run at 12 from seed i tried hempy (which is not the fit for me) I started trying to feed as if i was still running a veg cycle for a few weeks... (correct me if im wrong) but you have to feed them a little more from the get go because your trying to get as much vegetative growth as quick as possible.
I would maybe suggest checking that runoff pH, check your nute level and make sure your not just under feeding, and if that doesn't work it may be time to pot up. just a friendly suggestion. I think i will go try and take a pic of my sour candys ... the hempys look like dwarfish compared to my dwc buckets lol