is that powdery at end of leaf? midlew, if so.. and of course if you haven;t dropped anything like DE on it or soemthing.
could be from soil. Allow it to dry top 1" before watering if you don't already. when you do irrigate or fertigate, make sure 20% runoff is occurring. I think this will clear up in a couple weeks if you do that.. i had a similar problem in coco recently.
now, if it takes a nosedive or ramps up, re-assess... could be wrong.. looks like it isn't nute-related, though. leaf looks great, otherwise. full, lush etc..