sry didnt have time to read the whole thread, but everyone on the 1st page besides monkey should not be helping people at all in the plant problem threads until they know what they are talking about.your foliage from your pictures is damaged on the bottom, OLD!!!! LEAVES/FOLIAGE.
NUTE BURN will start on the new foliage....TOP LEAVES/FOLIAGE ASAP........so it starts from the top....
to my eyes that looks like either a MAG DEFF or some micro DEFF. Good luck pm me if u need more help.