Brown Spots, Nute Burn? Help... PICS

Hey i have a plant that i lst'd and is doing pretty good. Acouple of days ago brown spots started to appear on the fan leaves, since then they have spread a little, i was just wondering is it was nute burn or some thing else, maybe

I am using MG flower nutes 15-30-15 at 3/4 strentgh

i WAS feeding every watering until i heard that was bad so i have watered with just water for the last 4 days.

Can any one help me?

WOW,, they look just like my blueberry plants looked,,, how hot is your room,, looks a little like heat stress,, but I cant see enough of them so that is just my opinion.....Peace....................

i dont think its heat stress cause my room never gets above 86 degrees. and the tops of the plants are fine, (closer to the lights) but the lower fan leaves are going brown