Corid is a vitamin B blocker. All strains of coccidia including those that target other animals, thrive on thiamine. Corid is blocking that so the coocidia can't carry out their life cycle. Sulfa and Corid are a combination that is often used successfully to head off inflammation of the intestines, and it will kill any bacteria that tries to take advantage of the inflamed tissue.
Your chickens will be fine with the treatment you're providing. It will be under control very quickly.
Your chickens will be fine with the treatment you're providing. It will be under control very quickly.