I'm not sure what the symptoms are necessarily, but I have read from more than one reference that Flame Angels are really sensitive to elevated levels of copper. Like everyone else said, more info would help in diagnosing, but that might be something you'll want to check. I think anything close to or above .15 is considered very dangerous for them.

Have you done any copper treatments to the tank recently? You could also be getting gradually increased copper levels in your tank from the tap, if you're not using RO/DI filtered water.