it looks like heat but do what moodster says just to make sure. usually if its nute burn or a deficiency it affects most the leaves just not the extreme tips
how long ago did you feed them? if it was a couple days dont worry about it. a few hours, keep a close eye on it. what lighting are you using and how close are they
im using t5 flouros about 3-4'' away. ive given some strong bone meal tea a few times which could be nute burn. ill take it easy next time and leave out the bone meal. i got some less extreme shit. seaweed liquid and alfalfa.
ya im thinking nutes also, because im seeing it on the lower buds that are 2 feet away from the lights. i was checkin the net and found this. could be zinc deficiency? i gave it a bottle of water with liquid seaweed in hopes of fixing it. if it dont fix it i will try alfalfa. http://forum.grasscity.com/sick-plants-problems/246040-deficency-nute-burn-pics.html
Doesn't appear to Mg def to me. I would stick to the plain water advice, if it continues, then seek other remedies, I have learned that less is always more! so be careful with additives and remedies.