I'd post this in plant problems. Itll get more attention there. Also, you're going to need to post more than a photo of a leaf. Info on your grow...medium, light, water, nutrients etc.
My novice opinion with very little Info to go from, either a ph problem, salt build up, or potasium def. To get real help though, post in the correct sub forum with more information.
If you haven't seen these, they're a good quick reference...