I'd go with mg deficiency too but low mg signs start in the older leaves first and yellow from between the veins near the tips and edges of the leaves working toward the petiole. Your yellowing seems to be starting from the petiole and working out to the tips in younger leaves mostly. This would indicate an iron deficiency to me.
Any time there is a deficiency in mobile nutes, NPK, Mg or Zn the oldest and largest leaves tend to be affected first as the new growth steals from them to keep growing green and healthy. They'll get sick later as the deficiency progresses. With immobile nutes, Ca, Fe, S etc it's the newer growth that is first affected as it can steal those from elsewhere on the plant and if there's none in the soil they get messed up while the older ones look fine as they already have theirs and aren't giving it up.
Most good CalMag has iron in it so some of that would help or even an iron supplement from any garden center as they usually have it for lawns etc.
Higher pH can lock out the iron and other minerals too so make sure the pH in the root zone is 6.5 or lower.