First off, pot plants like a fairly consistent pH range......zero it in and keep it there. 5.6-5.8 for hydro, 6.3-6.5 for premix and the like.
It looks to me like the beginning of an CA deficiency but I agree with other, it looks like something on the outside of the leaf too. The rust spots is a calcium deficiency though.
We need a lot more info on your grow to answer correctly though.