When the lights came on in my tank this morning my yellow tang was barely swimming. Just swimming in place. Then would start to float on its side. I knew it wasn't good. He seemed like he had a white tint to the lower half of his body. Had to go out for a few hours. I came back and he was on the bottom of the tank with the clean up crew going to town. My wrasse and him were joined at the hip. He was ripping the hermits off him. And trying to lay on top of him. I'm so bummed. This fish has been in my tank for a year now. I haven't added a fish in 6 months. A few coral frags 2 weeks ago was the last addition. Tested water 2 days ago and everything was the norm. 5ppm nitrate. No ammonia. No nitrite. Cal 430. Alk 8.2 Mag 1480. Phos .08. The tang was perfectly normal at 8pm the night before. Fed the tank. He ate like a horse. Nori then mysis and brine shrimp. Then he and my wrasse swam around the tank as usual. Every other fish is normal as usual. Any ideas. Nothing has changed in my tank in a long time. Can figure this out. This is my first saltwater tank. Has been up a little over a year and the first time I lost a fish in this tank.