Hey mate. Wish I could help you with the yellowing. I don't think I've had that particular flavour of yellowing, though it's totally possible I did have it a dozen times and just ignored it and/or forgot I did. I almost feel like I remember seeing that kind of patchy thing - but who knows what I remember anymore vs the shit I just made up. Not me. Making shit up is way more convenient + better for the self esteem so it's become a bit of a habit.
It's not typical mag deficiency which tends to affect the lower leaves and yellows up the edges all around the leaf.
I've had iron deficiency which was from high ph and causes bright white/yellowing in the top growth. That's not what yours looks like though.
If the ph is good and it's not getting worse then I'd just make sure to keep up the calmag levels and keep an eye on it.
I like the fan arm a lot. I go through so many fans it's crazy. Will have to save money and try to get a good quality one or two someday. The fans they sell here are cheap crap. The garbage man has started to comment every time I bring a fresh mountain of busted desk fans out. So it's gotten to the point where I'm constantly hoarding them till I can find time to do a dump run. Broken fans are everywhere at my place.
I wasn't 100% sure from staring at your pics but it looks like you have the fan upside down? I find that the shitty plastic gears which create the back and forth oscillating movement, always strip easily. I'd be wary about having them any position other than vertical because it puts more stress on those parts.
There was a grower here a couple years ago who screwed his fans to the ceiling. I thought that was so cool. Till I tried it and had non-oscillating fans within a couple days.
Cool hempy setup.
Tead 'floats' them out when he transplants. I found that even messier than just dumping them out. But if you let them get very root bound they're ok. Also- the stuff is impossible to overwater- so you don't really need to do the regular upcan thing anyway. Looking good. Can't remember what else I was going to say