Hi
@Peak81! Genetics, cold temperatures, cold solution/medium, or a Phosphorous deficiency can lead to purple stems. In your scenario, it's certainly temp-related. Is your daytime temperature 10°C? What about the night temp? That's under the safe zone, 15°c is the ultimate threshold where you won't encounter issues. Hopefully the sun is going to fix this next week. Keep us up-to-date and happy growing 👊