From what i've read, foliar feeding should be about once a week, and its also best to spray with just water the next day to dissolve any undissolved salts left on the leaves. You mentioned a purple stem, it can be a deficiency but some strains have naturally purple stems. You should be watering every 3-4 days depending on the size of the pot. Also its best to spray just before or after the photoperiod when the majority of the stomatas are open, temps have to be below 80f or they tend to be closed.