Just off hand, some strains turn purple because of my A/C being cold. Some turn because just not enough nitrogen. Then some strains the PH may not be where they like it and not uptaking nutrient.

The trouble shooting form will get you more help.

If you have A/C and it's around 70 degrees and everything has been going alright and they are still looking good and growing then it's the temps. Nothing to worry about.
LOC NAR on probation Reviewed by LOC NAR on probation on . purplish looking stalks problem :wtf: My plants are in grow stage. Things have been going really good lately. Now all of a sudden the stalks are turning a purplish kinda color, going up the stalk. Some of the stems have a dark purplish color too. WHAT IS THE PROBLEM? I have looked at a few sites but all the info conflicts. I really do not want to kill them (duh) lol. They are under a 1000 metal halide bulb and I am using the general hydroponics feed schedule for mild growth. They are beautiful, growing, producing new Rating: 5