I found my biggest angelfish, Abby, dead this morning. She had no signs of disease or injury, so I'm not sure what happended to her. The water checked out fine. I've only had her for a year, so its not old age I don't think.
She was not too small when I got her...maybe about 3 inches tall...or around that, so she could have been older than I thought. Its just a mysterious death though.