Because the cations on the exchange sites are held reasonably tight, washing coco does little to change the makeup of the cations on the exchange sites. The washing will change the EC but not the CEC. CEC sites have a preference for some cations over others.
If the cations of Ca, Mg, Na and K are all present in the solution at the same concentration, they will be adsorbed at different levels, with calcium and magnesium being adsorbed at double the rate as they both have a double-positive charge, while potassium and sodium have a single-positive charge (Ca++, Mg++, K+, Na+).
I believe this is why I have a deficiency in the first place. Knowing this means the cal mag I am adding is being absorbed and making it unavailable to my plant.
How to correct is the next issue. Since my coco is known unbuffered removing cal mag is not the answer but adding more will not help my plant until the coco is full which took 4 months of feeding at 500 ppm in the study.
I decided to try my grandmothers way and foiler feed my plant with epsom salt.
I did this last night and my plant looks great this morning (Not Dead) and we will want to see if the spot slow or stop.
Thanks for all the help!
https://growdiaries.com/diaries/8001-lennuts-first-grow