This is my first grow and my plants are about 1 month old. I've noticed that most of the stems have a purplish tint on the upper half (the half that points towards the light). I was wondering if this is natural or is something wrong with my light setup? I have a 400W MH bulb about 12"- 15" away from the top of my plants. The bulb has a fan blowing right on it so I believe it's nothing to do with heat, but I'm not entirely sure.