It looks like you're overfeeding judging from those photos. The dark green, paper dry leaves are obvious signs of overfeeding. Ignore the patches
and burn spots and judge the new growth once the plant recovers.
Mag deficiency looks like yellowing between the veins of the leaf and purple leaf stems and branches.
You can see the yellowing starting between the viens while the viens stay green. If you could see the stems in the picture they have purple streaking
and the leaf stems are completely purple. Mag deficiency stunts growth for a while and is so easy to treat so you should never let it get to this point,
all you need is a $3 bag of epsom salts and a spray bottle.