I don't do hydro nor coco, but:

Do you spray the plants with anything?
Are there adequate drainage holes, or is the rootball sitting in water at all?
What is your ingoing water ph? Coco requires a lower water ph than soil.
Perhaps you bent/folded some roots during transplant? What do the roots look like now? (pop 'em out and look) Should be healthy white.
Why did you add a "heavy" dose of CalMag? Too low of a ph level can lock-out calcium, and magnesium is a salt. (coco retains salts)
Rusty Trichome Reviewed by Rusty Trichome on . Doctor Doctor! Yellow and Brown Make me Frown :( got 3 Violator Kush babies rolling. 2/3 look perfectly healthy. 1/3 looks like this! Information: started about five days ago. At that time i was not feeding them anything except distilled water. they are sitting in party cups, in jiffy pucks that are surrounded by cocoa. after i saw the yellowing/browning, i quickly made a 1/4 strength nutrient solution with a healthy dose of cal/mag+. Since then the affected bottom leaves have withered to what you see, and the set directly above have Rating: 5