If they are a week old, they may be suffering from a respiratory problem from where they came from, but if there is any spilled water in their bedding ( which is a constant problem in brooders,) they could be suffering from brooder pneumonia or aspergillosis from mold. MG or infectious bronchitis can be passed on from other chickens raised near them, and MG can be passed through the eggs.Hatching conditions could also have something to do with their illness. Make sure that they have good air circulation, remove any wet bedding, and keep everything as dry as possible. Coccidiosis is more of a problem in slightly older chicks, who have been exposed to dirt or older chicks. I would take each weak chick, and make them drink some vitamin/electrolyte solution (such as SaveAChick) or something similar such as Pedialyte or Gatorade. Treating them with Corid will not hurt them, but I kind of think they are a little young for coccidia. I hope this helps.
