I agree that you can add some sort of vitamin/minerals to water/food. Gatorade and pedialyte can work but can be an expensive way to add electrolytes. A more affordable way may be to supply your chicken with electrolytes from opening up electrolyte replacement capsules and mixing it with the water. Have anyone tried this before?
I use the pack from the feedstore that says High Performance Poultry Pak made by Durvet seems to be pretty good for my chickens. I also like Save-a-chick.