Well first of all you should quarantine any sick chicks so that it doesn't infect your other birds. If it's not thriving then something is obviously wrong. The times my chicks have puffed out they have had Coccidosis......generally I avoid this by feeding medicated scratch when they are first born for a couple of weeks. I would imagine it has either recovered or died by now. Try the medicated feed in your hatchlings to avoid recurrence.