it's look like low Nitrogen to me. I used to have something like this so i put 29-10-10 fertilizer for a couple weeks, and move the light and bend some stems in order to make most of the leaves recieve the most light then it was gone.

I don't have any idea about the pH so im not sure but you may try my solution. i still have a few(just 1 or 2) of leaves like that.:rastasmoke: