How long has this system been set up?
What size system with how much live rock?
What are your ammonia, nitrite, nitrate levels?
Are all new additions quarantined?
How long did you have this fish?
Did you notice any abnormal behavior or external symptoms prior to death?
Did you notice any weight loss?
Have you had any other recent fish deaths? If so, to what did you attribute those deaths?
Have you witnessed any aggression between these fish?
I think answers to these questions will get us closer to figuring out what happened.
What size system with how much live rock?
What are your ammonia, nitrite, nitrate levels?
Are all new additions quarantined?
How long did you have this fish?
Did you notice any abnormal behavior or external symptoms prior to death?
Did you notice any weight loss?
Have you had any other recent fish deaths? If so, to what did you attribute those deaths?
Have you witnessed any aggression between these fish?
I think answers to these questions will get us closer to figuring out what happened.