What are you feeding it? I agree, time to transplant. Some of the leaves look really pale but i dont know it that is just the lighting or not but that could be nitrogen def. Like Rwise said, low temps bring out the purps! Got it on my Sour D atm. Cant tell right now if it's a problem or not. If it gets worse or other symptoms pop up then you have an issues but if they are healthy otherwise then you should be fine.