Curled leaf problem

This is our 5 week old northern light. It has been doing great but I just noticed that several leaves are starting to curl up and the tips are brown. The ph is fine, it is not over watered or too hot. Any suggestions?
Thanks

looks like you light burning them alittle but i cold be wrong if its on the bottoms leaves aswell!!!


THEN IT i think is it Potassium deficiency fosho.


more pics would be great

salt build up will do this as well along with other things