No, Corid will not harm them, even if they don't have it, but you can lose them if you don't treat it. Corid is not an antibiotic, but blocks thiamine in the organism that causes cocci. What symptoms are you seeing? Lethargy, not eating, hunched posture, runny stools with mucus or blood, can all be symptoms. Dosage of Corid is 1 1/2 tsp of the powder per gallon of water for 5 days.