Thanks all for your help.
As it turns out, I happened upon some Sulmet finally and started them on that because it can treat coccsidia and I now have it easily at hand.
I don't know how old these new chickens are, probably 2 years or so I would imagine, because they're debeaked red laying hens...
I'm pretty positive that 2 new chickens that my friend got (yes I know one shouldn't introduce 2 adult chicken strangers to a flock, but what's done is done) have coccidia, judging from the blood in their poo (I'm farmsitting for my friend).
They are separated now and I'd like to put them on...