I didn't catch what kind of light you have on them. With 30" plants, you can get yellow leaves at the very bottom just from lack of light penetration; probably need 600W or more to maintain leaf vigor all the way down a 30" indoor plant. But yeah, I'd ease up a bit on nutes.. like 1/4 strength every other week, and just keep an eye on that little "claw thing" the top leaves have got going on there.
I just noticed, too, that you reported using MG potting soil. Are we talking the pre-ferted stuff that says "feeds for three months"? If so, they are DEF getting too many nutes. That stuff is good thru a full grow, so the Dutch growers say (and who knows more about indoor growing than the Dutch?).
You're walking right in my footsteps that I just laid down about 2 months ago -- sativa dom's in MG soil, adding FF nutes every other watering... Wanna see my pic's of my plants I almost blew up this way?