Potassium?

you'd probably see more damage on tips, if k-def. i'd wager P is a tad high. This can lockout Ca, which would cause the dots, and also potentially 3 other things that can cause interveinal chlorosis - zn, fe, and mg that lower yellow leaf.. did it pale interveinal at first or tip-in.. if tip-in add a little N, too. gotta play with dosing of various products used... try to do those things without drastically changing other things too much. take notes of what you do.. see what happens over 2-3 weeks and go from there... any nosedive and you would obviously react sooner.