Red stems? What’s causing it?

I’ve been noticing my stems are turning red lately not all of them but a few anybody know what’s causing this and is it anything to worry about?

I had that in one of my grows. The different forms that I've done research on go back and forth as to what kind of deficiency it is. I continue feeding mine and taking care of it like normal and eventually it went away. Not sure if it's good advice but that's what I did and my girls are fine.

Mine clears up wi th bone meal