When my chicken died of it none of the other birds showed symptoms. I had chicks at the time that had been with her and I treated them all at the same time. She was too far gone when I started so she died but the chicks are all full grown laying hens now.
They don't always have bloody poop. You can spend a bunch of money to take a chick to the vet to get a fecal test done. Or you can spend like $16 and treat them with corid. You will have to treat the entire flock and they can't have another water source during the treatment. Don't provide any...
So we can try to tag some people for other advice but in the meantime you should do some research on coccidiosis and see if it sounds familiar
@azygous @Wyorp Rock
Yeah coccidiosis would not make them drop dead overnight. It takes a while. I had a full grown hen die of it and it took a couple months. It is a parasite and is found in all soil. Chicks have no resistance but older hens do. Slowly introducing chicks to soil can help them build up resistance...
Is thier first exposure to soil? Coccidiosis can kill chicks pretty quickly and they are more susceptible because they haven't built up any resistance-especially if they haven't been exposed beforehand.