Glad your chick is improved so quickly. I would continue the vitamins for a few days at least to ensure that any deficiency is really reversed.
A couple of comments based on your picture, the towels in the bottom of the cardboard box are very wet. Wet brooder conditions can really cause problems and illness in the brooder, coccidiosis being a big one, or your chicks getting chilled. Everything needs to be kept as dry as you can. They are also going to outgrow that box very quickly. Something that will not absorb water is better than cardboard, and raising the water up a little, can help keep them from running through it and spilling it. I usually use a brick or block of wood to raise mine up. You are also going to need a bigger water container very soon, make sure it's one they can't drown in. Once they are eating well, keeping the feed in a feeder will help keep them from eating droppings contaminated feed also, which can contribute to coccidiosis out breaks. Chicks can be very messy. Best of luck with your babies, hope they continue to do well.