Sick birds don't drink enough, so if i were you I would give the sickest chicks Corid 0.02 ml (~1 drop) per 100 grams of body weigh orally. Do this once or twice daily. Do this in addition to the 2 teaspoons per gallon.
This dose is based on 20 mg/kg.
You could also give them Tylan 0.02 ml (~1 drop) per 100 grams of weight orally three time a day.
This dose is based on 36 mg/kg.
I suggested giving the Corid and the Tylan because coccidiosis and necrotic enteritis often go hand-in-hand. The to medications are safe to use at the same time.
