I know it's been a year, and this is not really a concern anymore, but just for the record, judging by the appearance of your bottom leaves, it is for sure a potassium deficiecy causing the purple color, potassium is known as a color changer, and can be used as a cosmetic effect to your buds...
if it is not overwatering, spots and burnt tips sounds like either potassium deficiency or nitrogen burn. potassium is characterized by the little leave edges curling upward and yellowing, the old parts showing symptoms will not recover, if they are badly damaged clip off the leaves and watch...