I would need to see your entire feed schedule but too much Calcium and Magnesium can be locking out your K. The other thing is genetics and the natural fade at the end of the plants life.
0-50-30 is very strong and it would be easy to overdo it with that product. Nutrient "Balance" is key.
The proper use of “salt” based fertilizer to grow Auto Flowering Cannabis. Salts: Natural and man made any chemical compound formed from the reaction of an acid with a base, with all or part of the hydrogen of the acid replaced by a metal or other cation. Learning how to use salt based...
www.autoflower.org