Not totally necessary but adding vitamin supplements or electrolytes to their drinking water will certainly do no harm.
It is possible that this chick is at the bottom of the pecking order and is not being provided enough time to eat. There are a few things that you could do to help. Make sure that you are providing enough feeder space for all of the birds to eat at the same time. You could separate the smaller chick from the other chick so that it has an opportunity to eat without interference from the other chickens. Finally, be sure that the chick is not exhibiting signs of illness.