lower nighttime temperatures sometimes cause purpling (purple is just a color, has nothing to do with potency, anyway) ... if your temps drop below 70 degrees, growth slows, accordingly ... also, avoid over-watering, allow the plants to dry between waterings ... do not feed, until the plants are two weeks old, and half-strength thereafter ... more damage is done, with overfeeding, than harm from under-feeding ... good luck :smokin: