That is a crazy looking yellow tang. I hope it can recover! My Yellow Tang had a similar issue (bloated and don't eat for 10+ days) but not as extreme of a case. I tried feeding LRS, herbivore feast, TDO, and frozen mysis which it was excited to see but did not/could not eat. I also bought one of those circular brine shrimp hatcheries and started feeding that as much as I could (ie, 3-4 days a week depending on hatching schedule). Eventually the tang started eating the small brine and picking at the rocks. Initially it looked like the tang was as just going through the motions and not actually eating anything off the rocks. I think this is because it wanted to eat but could not do so. Eventually it started pooping and eating.