Medic! Plant Down!

Hello all. I was given a plant "K2 breed" 1 month ago at which that age was 3 weeks. It had a lot of dry,dying leaves at the bottom and were curling. The guy told me he was using 12-15-12, so I figured nitrogen def. and purchased 20-15-10 and everyhing was ok til last week. Sorry no pic but bottom leaves are drying out and curling yellowish color. I only feed when soil is bone dry. Mg deficiency? If so what is high in mg?

could be over watered.

are you mixing your nutes full strength if so could be nute burn or could be just that the lower ones arent getting any light hard to tell without pics