Well I'm Not sure as noone could be but 1st look I would say either nute or overwatering what kind of water schedule is it on more info is better! Ph is the start to alot of probs! DaMilkman
I thought it looked like magnesium too but i've been feeding it full strength so i dont know. Could low humidity have anything to do with it cuz the humidity's pretty low (25-30%)
The wierd thing is its the only one that looks like that and its being fed the same as others and in same conditions
Same conditions? Are you sure? Same pH, same nute levels? Are you sure you don't have a chunk of bad coco in there? There's obviously a difference. If may be bad genes or a pathogen, but the odds are in favor of issues with the medium.
your plants need transplanting , they are root-bound !!! & the light is probably too close ....its look's more like light bleaching to me , then another thing ....a mag deficiency starts with the older leaves & not the tops & fresh leaves so raise your light up , to about 80 cms above the plants & transplant immediately ...or the plant is going to start to burn & it will be dead in 1 week also those damaged leaves , are damaged , there is no fixing them now ...they will eventually get worse ......so just pay attention to the new growth peace John
what light are you using by the way ??? ...because it could be just that there root-bound if your using fluoros then they wouldn't cause light intensity bleaching
im using flouros and it is not rootbound becuase I have a plant twice the size in the same container and it is not rootbound. I think I shocked the plant when I changed the light cycle from 18-6 to 24-0.
you didnt shock the plant man from changing the light schedule you have 30 day old plant's at least there ...in what are those 10 ltr or 5 ltr pot's ...that are half filled with soil .....they have rooted the pots & need to be transplanted peace John