To be clear... coccidia, as far as I know are found in EVERY single chicken poo and all are exposed from day 1. It is only an issue when they have ingested too many sporulated oocysts (eggs). Then their immune systems are over run.I would go get corid and treat the rest since they have been exposed.
Blood in the stool is a sign that it's worse than you would hope. The intestines are under attack and the lesions created are bleeding. If too bad... that portion of the intestine *may* become necrotic (dead), and never able to absorb nutrients in the future.
Some birds will have stronger immune systems and fight things off better. So they may not be showing the signs. But yes, it is true they will hide things as well as possible in order to avoid being preyed on first... or even by their own flock sometimes.

There have been PLENTY of times I wish I had acted sooner!


It is true that Corid is safe to use on all chicks even if they aren't showing signs. It's important NOT to supplement vitamins during this time because it works by blocking thiamine (a B vitamin) to starve out and SLOW the growth of the coccidia while the chickens immune system build MORE resistance.