Could this be from a combination of...

Overfertilizing (liquid miracle grow bottle says once every 2 weeks, I use 1/4 dose every 2-3 DAYS)
Overwatering (some posts say to wait until the top 2-3 of soil inches are dry.. I always water when the top 1/2 inch is dry)

It appears everything on the BOTTOM is dying, and working its way up. I don't know what they mean when they say "nute lock", but maybe the bottom leaves are absorbing too much nutrients and dying? And the top are doing fine because they're farther away?