You don't need to keep your chicks separated from adult chickens because the adults have probably already built up a resistance (sort of immunity) to the type of protozoa that infected your chicks with cocci.
Hello mlove, Corid is supposedly not supposed to be the best thing to treat your birds with. I did some research on it and here is the link to the forum with the explanation...read the last post on the last page...its mine. Good luck!!
I think you will find opposing opinions on that, and sometimes it is a matter of what is on hand and what can be gotten easily. Sulmet is readily available here, and yes, it works, and works best on severe cases. Personally, I use the Amprolium as in the long run I feel it is the lesser of two evils.