Are you sure it's not a slight lock out due to ph?
Try a foliar feed of Epsom salt. Heat a liter of water on stove, add teaspoon of Epsom, disolve completely, let it cool to room temp. Put in sprayer and spray leaves top and under. Best time is right before lights out to avoid any spot burning.
Based on the pics, magnesium isn't the main issue. The leaves are showing a potassium issue. You have yo figure out why something is happening before you treat it. 99% of the time, adding more of something is the wrong answer.