The rule of thumb is you never put larger chicks with smaller chicks they will bully until the smaller ones are dead. when the smaller ones are full of strength and grow nice wings and shoulder feathers that might be a good time to introduce them but supervise it carefully, if there is any pecking at the feet,beak,eyes, or head aggressively then you need to wait a week then introduce them again, what I did since I didnt have two brooders is I just put distractions in the brooder such as duct tape, they like shiny things, and you can also put a button on a hanging string, they like things that move because they like to chase, and every morning I also cut some thin grass up as small as I can get it and sprinkle it all around the brooder and they actually get there vitamins and protein they need through little bugs you find outside and grass. so there is no need for medicated water or food, you just need to give em a taste for things outside. Hope this helped, much love