Ive had and not had purple stems with bagseeds and fem seeds. I think it is just genetics.Purple stems are also a sign of bad genetics.. I had used bagseeds my first 3 grows, they all had purple stems.. My last grow was with quality seeds and had no purple stems.. And the purple stems also have no negative effect on your bud.. So you are in the clear man.. I wouldnt worry about it.. People say purple stems are from a deficiency, OF PRETTY MUCH EVERYTHING.. Hard to diagnose..