You treat for 5 - 7 days with the dose given before. If they are slow to recover then you can do a second 5-7 days at a lower dose (1/3 tsp of the powder per gallon of water). It very much depends on the strain they have and how much damage is done to the digestive tract. I usually have only had to do the first 5-7 days at the full dose with the strain(s) I've dealt with. The decision should be based on how the birds are. Whatever strain(s) they are exposed to, they should be resistant to those in the future. New strains could make them sick (new strains can be brought in with new birds or if birds are moved to new ground). Corid is very safe, if in doubt I would treat. The Corid kills the coccidia present, it does not provide protection for future exposure. If you sell the birds I would just tell them that they've just been treated for coccidiosis, and tell them what to do if they see symptoms, assuming that they don't already know how to treat and what to watch for. Coccidiosis is very common in chicks and young birds.
