This is a stressful situation, I’m sorry you are dealing with this.
Pictures would help, but for sure more information would be useful in supporting your search for answers.
Why are you assuming nutrients? Pro Mix and
Fox Farm too is a solid solution, but I've been using Ocean Forest and
Happy Frog since the 90s and the results have been solid. One time I was quick to blame
Happy Frog for similarly discoloring my cuttings, but after thinking it through, I realized going from florescent lighting in peat pots, to transplanting into new pots, and then putting them under more intense light without giving them a period to adapt was too much. I had done that way several times, but one plants stress will delay growth, and another’s will kill it.
It’s the same with as with other things we do to them that cause stress. Just because it worked before… It may be less stress on us, if we stay aware that there are times we are disrupting their lives and remain ready to accommodate them when it’s too much.
When you say, “…deficiency’s immediately with new growth. Brown spots forming yellowing leaves extremely fast”, what do you mean immediately. Is it hour, days, or as soon as the new growth comes in?
Is the old growth fine, and only the new growth that has the brown spots and yellowing, or is it spreading to the old growth too?
Is the soil a new bag, or has it been stored properly if not?
Did the transplant go smoothly?
Has the environment changed otherwise, the light intensity, air flow, humidity, VPD.
I am new to this forum and don’t mean to be invasive or pushy, but I think answers to these questions would be helpful for the other readers help you find some peace.
