I have also chosen to not give my flock medicated feed. I've raised chicks 4 times, and never had an issue with coccidiosis on non medicated feed. When I went to the feed store to buy feed last spring, they looked at me like I had 2 heads, and tried very hard to tell me that all of my birds would die if I did not give them medicated feed, and why would anyone choose to do that, and blah, blah, blah. I stood and took it until they had run out of their blah, blah, blah, (because i really needed to go home with a bag of feed that day) then calmly asked them what other kind of feed was available for chicks. They reluctantly sold me a bag of multi-flock raiser, which is higher protein than the chick starter. IMO, a far superior product. My girls were all laying at 16.5 - 17 weeks. So, my advice is, stand your ground. The feed store employees are merely giving you the party line, and honestly, I'm guessing that for the most part, it is just a job for them, and most of them have never raised a chicken, or any other livestock animal for that matter.