I suspect it could be cocci. You might have to administer the corid treated water via eyedropper since the chicks are probably too sick to drink the treated water on their own. Place a couple of drops on the side of the beak, you might have to manipulate the beak to open to get them to swallow. Be careful not to aspirate them with too much of the liquid. Do this until they are able to drink the treated water on their own. Remove chicks from the brooder. Disinfect the brooder, waterer, and feeder with ammonia water solution, not bleach. Rinse and dry everything thoroughly before placing the chicks back in the brooder. Give them fresh water and feed. Do not give them vitamin supplements including nutri drench while treating for cocci. You can try giving them buttermilk, not yogurt...if you wish.