It's normal for plants to discard lower leaves that aren't getting enough light, but something does seem lacking there.

Initially thought "P" but looking at your additives it wasn't that.... so I went back over this Text and think it might be Mg "magnesium"

Ok, there's my :twocents: I'm not a pro by any means.
canniwhatsis Reviewed by canniwhatsis on . Help with Unusual yellowing of older growth + rusting inner ridges (PICS) What is your experience level? Novice Your Equipment: .1) Type and wattage of lights. 400W CMH .2) Distance from tops? 20" .3) Reflector type? batwing .4) Is there a consistent fresh air supply? yes .5) Do you have an exhaust fan and a circulation fan? yes Your medium: Rating: 5