Medicated food is a coccidia PREVENTATIVE but it is NOT a curative dosage. Hie thee to a feed store and get a product which has the active ingredient amprollium (ie corid (even if labelled for cattle/sheep use) or amprol). There are other coccidiostats based on sulfates, but these can cause liver damage and intestinal irritation (such as sulmet), so, if available, an amprollium based drug should be your first try. Realize that by the time they are bleeding quite a bit of damage is being done, so the sooner you can start medicating them the better. You can continue using medicated feed. DO NOT give vitamins if using amprol or a medicated feed as the coccidiostat functions by starving the coccidia of a type of b vitamin they yse heavily, but which is not AS essential to the chick.
Good luck!
Good luck!