Leaf deficiency

Mag mobile, calcium not, the relationship although beneficial is also antagonistic meaning too much of one or the other, things get screwy, 18 days of questions with no selected answers, looks like you have been fighting high salinity in soil for a while, need to take a reading and leech water until EC reaches recommend level, when the salt content of soil is too high it reverses flow of water and prevents transpiration, no transpiration, no uptake, high ec normally comes with skewed ph.

Was their anything else in the Mg rich solution you fed them? and did you get any runoff?? what was its PH??? Maybe the last irrigation pushed out the other available nutrients and gave it a PH swing in a direction it does not like? No Diary hard to tell. don't know what your feeding them or how your growing them so hard to tell. Can guess but it could very well be something else. https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg Here is a leaf chart that is helpful. Good Luck!