My only other thought is possibly roundworms, since it has been so rainy/wet for you lately. Not sure it would make it that bloody, but evidently it can cause bloody stools. As can hairworms.It’s difficult to get these things here. Most time one needs a vet to prescribe any sort of med. I am just lucky I had the sulphatrim left from another chook.
My horse vet is good with prescriptions that I need for horses or chooks.
And in Canada there is an egg with-hold when treating with Corid. I think it’s a couple days.
Not that the chicks lay eggs haha.
But if there is coccidiosis then I want to treat the flock.