Nitrogen toxicity (burning) from feeding too much or too often, or both (or a too hot soil mix).
Cut your feeding strength in half and they should be fine, but stop feeding them for 10 days first, they need to use up what is already there before any new nutrients are added.
Being "Maui Wowie" it has a large percentage of Sativa genes and Sativas require a lot less feeding than indicas, especially nitrogen.
If it was a potassium problem (which it is not), cal/mag would not have fixed it.
Remember too, in soil it is plain water/plain water/feed/plain water/plain water/feed......... so that your plants are only being fed every 10-14 days, this is plenty, as soil "holds onto" nutrients better than any other substrate.
Also, in soil your pH should be between 6.4 and 6.8 - 5.9 is way too acidic.
So, to sum up, reduce your feeding and up your pH and things will improve rapidly!
Hope this helps, Organoman.