Thank you, I suspected as much to be honest, it's very small compared to the others that hatched.
I haven't culled a chick before, what is the best way to go about it? I've read about using vinegar and bicarb to create CO2, is that a humane way to do it?
Actually don't do that, that suffocates the chick to death with carbon dioxide. A buildup of carbon dioxide in the body is what drives you to draw a breath, so as you can imagine the chick would be aware it's suffocating and that's not a good way to go.
If you want to go with a method that's similar but humane, pick up some starting fluid that contains ether. Ether used to be used as an anesthetic in veterinary medicine, and it simply puts the chick to sleep, and then it dies peacefully, unaware that anything is going on.
https://www.backyardchickens.com/ar...re-culling-the-injured-and-sick-babies.72140/