A hernia, when I've seen it in my chicks, looks like bloody tissue poking through the navel. Sometimes, unfortunately, the intestines also come out. Sometimes it's just a small bloody little knob that dries up and disappears in a few days. The yolk sac, however, looks more yellowish or whitish, maybe with a very few small blood vessels, and it's attached to the navel by a thin string of whitish/gooey membrane (the cord). It too will dry up as the chick absorbs the remainder, or it will fall off. That may not be 100% accurate, but it's just what I've seen in my chicks. Can you post a picture of the navel?How do u know the difference in a yolk sac and hernia? I have one that I thought was yolk sac but I’m not sure now after reading these threads