yellowing new growth

Hi all, forum lurker here, read lots but can't seem to find the same problem. If you knew me or my attempts at growing you'd have already fallen out with me, lol, this is like my fifth or sixth try cos every time I get close to the end I always crop too early and smoke the premature buds and waste weeks/months of work and get a headache, feel crap and hate myself and lack of patience. The herb I'm trying to grow is for medicinal use and the pills I get from the doc are addictive and make me an angry individual. Anyways sorry about the small talk, my, ahem, set up is as basic as basic can be, self made reflector and cfl's, cpu fan and as yet just tap water. The new growth is coming in yellow, everywhere I look it specifies yellowing from the bottom not the top. So far I'm guessing either nitrogen or magnesium deficiency but the symptoms closely resemble light bleaching but from cfl's?, surely not...I've tried to keep them as close to the lights as possible and sometimes the temperature has got to low 30's. I is like a fallen tree, stumped.

it looks like MG def to me,

Thanks for the response, do I just start feeding her now, I was thinking along the lines of a little growth nute watered in and a little foliar feed as well, thanks for any response, consideration given, still trying to get used to a forum with good people on it, .