The feed bag might just say ACS. If it doesn't, try swapping to a chick crumb that does contain ACS (anticoccidiostat). That might be enough to get on top of the numbers they could have and help these little guys thrive.
All chicks have coccidia, but if the numbers get too high they damage the gut so the chicks don't thrive. ACS just keeps the numbers down. Different individuals are differently susceptible, just like people to diseases.