Do you mean feed with coccidiostat in it? Birds can only benefit from it when they are young as far as I know. Usually, older birds have already built up a resistance to Coccidia, but they can still get overrun by it, but less often. Also, if the bird is sick, they would need corid. Maybe that is what you are thinking of?
You can try getting them some electrolyte/vitamin mix and can give it to them in a second waterer. You also might want to give them an exam to rule out internal laying, or external parasites (let me know if you need to know how to do that). You can try to deworm them, too, but Gigachad is right, many chickens can succumb to diseases and issues in just a few years.