Not having a diary for your grow makes it VERY difficult to give you any advice here! Even if you only start the diary now, where you're at, it will help on down the line if you run into more problems!
That being said, I would first check the pH of your runoff to make sure that's in a suitable range (6.0-6.5). Depending on what you're feeding your grow, I would take a wild guess and say it's a bit of nute burn - leaning towards too much nitrogen... but again, I have no information that would lead me to say this is definitely your problem.
You could always do a good flush and then re-start your nutes at about 1/2 strength and see if the problems persist (you won't be able to repair the damage to these leaves but if the problem has been resolved, you won't see any further damage).
Good luck - and DO start a diary!