Red stalk

So i have a 2 foot tall hash plant and the stem turned red about a foot up and the new growth is growing fine but the red wont go away. Does anyone have any idea what this could be?

what lights are you using? if your growing under cfl the stems and branches turn red. my plants have a red stem and stalk

It's a switchable 400w I found out that it happened because its previous owner treated it badly.