Its most likely his gall bladder, the organ that controls buoyancy in fish. I would put him in a separate chamber or hospital tank and wait to see if it gets better. Try feeding him live food and high quality spirulina flakes (algae based).

Hope your fish gets better.


Ps. I have a coral beauty as well and it is an awesome fish. It took it a couple days to get acclimated but after that he started eating spirulina flakes and grazing on the rocks for algae and pods.