im growing in coco using cocoteks advanced nutrient feeding schedule, i follow water, feed, water. Temp is around 80-82 with the lights on and 68-70 with the lights off, these were gorilla glue #4 clones so not a purple strain. with a ph going in at 6.0Try giving some more info.
Are you growing in soil? What soil?
Hydro?
Do you feed them and if so, what do you feed them with?
Can you post picture of the fullsize plant?
What's the temperatures, your ph going in and out/ppm?
That would help a lot for anyone to diagnose.
Without knowing anything it can be everything.![]()
Knowing the purpling is not genetics I would start by adding calmag, as purple stems often indicates mag def.these were gorilla glue #4 clones so not a purple strain.