I have a juvenile bristletooth tang that was doing fine until about two days ago. He seemed to be picking at rocks/ eating fine as well as breathing at the right speed. The other day, I noticed a change in the speed of its breathing and now it is extremely fast. I can’t get it to eat. I put it in a quarantine tank with PraziPro to see if it would help, but instead it laid on its side and continued to breathe fast. I moved it back into my display tank and it began to swim back upright. None of my other fish are breathing fast and my parameters are all in check ( tested with salifert test kits). What could be wrong with it and what can I do.