Your pics show 2 deficiencies:
The general yellowing is caused by N deficiency, which is normal for large fanleaves if the plant is in flowering or the fanleaves are old and localized at the bottom of the plant. If one of these two is the case, don't try to fix it, it's normal, the plant is just sucking out the energy and nutes from the old leaves to redirect towards the buds. Completely natural.
The brown spots could be produced by a calcium deficiency. Are there more brown spots on other, healthy leaves? If yes, you can fix this by adding cal-mag or by adding 2 tbs/gal of molasses to the watering solution. If not, it's just a normal reaction to the N def.