That looks a possible slight Magnesium deficiency, but would love to see some better pics. Mag is one of the first nutes to get locked out with improper PH.
You can ID a mag deficiency by yellowing between the veins of the leaves (called, "intervenal chlorosis").
Make sure your PH is in range and it should work itself out, and adding a little cal-mag won't hurt. In the mean time, a foliar feed with epsom salts should help.
OH, just a minute...may i add to this. Ween, please don't give the Epsoms by foliar feeding . Give by spreading on the surface , or by mixing well with the next two-three-drinks. Giving by spraying on the leaves acts as a laxative for the entire system. Not good. It helps to mix them up in a glass of warm water first , it really speeds up the dissolve process, then mix that up with your feed water. Hope i havn't upset you Krip but this info came right from Doc. I used to believe as you only months ago , so...anyhow have a great Sunday everyone,...still have one more "sleep in" yeepa !