Corid (amprollium) is very safe to use if there might be coccidiosis. It is available without a prescription at most feed stores. Dosage is 2 tsp (10ml) of the liquid or 1 1/2 tsp of the powder per gallon of water for 5-7 days. If your fecal float comes back positive, the vet may want to treat with sulfa antibiotic such as Albon or sulfadimethoxine, since cecal coccidiosis is pretty serious. It is good, though since your chickens are not seeming to be act sick.
