I have about ten or more fish in my 125 and this tang was the oldest. He was the biggest and most aggressive. If I put a finger in the tank to feed them, Naso would nip at my finger every time. My dad went into the hospital Wed night. I feed the fish Wed afternoon and I didnt "examine" the Naso, but I believe was eating. I spent the night in the hospital Wed and Thurs night, but I went home Thurs to feed the dogs and the fish. I was in a hurry so I didnt notice anything wrong. Friday I got home about 5pm and my friend said "Look at the fish swimming sideways, how cool!" At first I thought nothing of the comment but when I looked at the tank I immediately noticed the Naso looking very thin and I could clearly see his spine. His stomached looked paper thin and I immediately fed pellets, mysis, and brine.
I went and got some filtered natural seawater from WB and siphoned water from my display into a 30 trashcan. I added a powerhead and a heater, and then the naso. I noticed my yellow tang was "roughing" the Naso up, and that had never happened before. I added the Naso to the trashcan Friday afternoon and He passed Sat night between 7pm and 9pm. RIP!!
I visited my friends house and looked at his tank last week and noticed his oldest Blue Hippo tang looked the same way mine did, and his died a few days later. Is this a case of old age?