mine are a week old and get both already. The last time this happened it worked well for me. Then again though mine are about 7 to 8 daysYour chicks do not need Corid. Corid is for cocci. They will not get cocci in two days. Most do not get cocci until they have been exposed to something from the outside, and it probably takes 6 days for them to build up to a harmful level. Corid blocks the absorption of nutrients - which slows down the growth of cocci. It also can cause curled toes and other defects in the chick. I would not dose with Corid unless they show severe signs.
You might want to add electrolites (save-a-chick) to the water to help perk them up. The home-made remedy is sugar water.
You can also add Apple Cider Vinegar to the water to toughen their intestines up (acid) which will help them fight off cocci later. I believe its 1 tsp per qt of water.