Looking at the surrounding leaves...it doean't look to me like overnute. Is this starting at the bottom and moving-up the plant? Overnute will start showing on virtually all of the leaf-edges, and get worse without correction. Heat stress usually starts at the top, and works it way down.
Possible rootbound...?

To me, it looks more like overwatering or root rot What do the roots look like, and what is your watering schedule? Are you letting the soil dry between waterings?

-or-

Are you spraying or pouring something on the lower leaves?