So your dose was correct. I'd just keep an eye on them and see how they do, it may just have been cecal poop. But occasionally you might have to treat with something like Sulfadimethoxine (sp?) if the Corid doesn't clear it up.
How old are these birds and what was the dose of Corid you were mixing up? Were you giving buttermilk, acv and yogurt at the same time as the Corid?
I have never had to do a repeat or follow up dose of Corid, once I treat it's taken care of.
You might try stopping the ACV, buttermilk and...