Okay you look pretty good all around. I was wondering if you had a pH problem that was locking out important nutrients, and/or a temps problem that was making you see symptoms even in a situation that would otherwise have been only slightly 'off'.
So just get going on that CalMag, and you can do a foliar feed with a micro supplement such as GH Micro to stop the problem spreading while your plant starts to uptake the new fertilizer.
The old yellow leaves won't heal, but new growht will be much healthier.