Coccidiosis is fairly common in chicks.
Treatment in the US is commonly with amprolium, often sold as Corid.
It gets mixed into their water for a certain number of day (directions should be on the package). It is available at many places that sell animal food.
When giving them Corid, do not provide any other source of water, and do not add vitamins or anything else to the water.
Corid (amprolium) is safe to give to chickens of any age.
If they do not have coccidiosis, Corid should do no harm.
Corid is not an antibiotic. It works by blocking a particular vitamin coccidiosis needs.
If you are not in the USA, you can probably also buy a medicine to treat coccidiosis, but it might be a different medicine-- different ones are common in different countries. Again, follow the directions on the package for whatever you get.
