I did not use medicated feed for my chicks when I got them. They are now 4 weeks, 5 weeks and 6 weeks old. Is it too late to start them on it or did I miss the window to protect them from coccidiosis. I did not get it as I was trying to keep them as natural chemical free as possible. Now I am hearing I should have done it and wondering if its too late or if it will make them sick to start them on it now.