I lost one of my green severums yesterday. The day before I did the weekly water change I noticed it's odd behavior, staying at the bottom of the tank in one place. The right side of it's face was a little darker than normal. Within 2 days the fish died and it's face was completely black. I don't know what could have cause it's death. Possibly it bumped into one of the large rocks in the aquarium and was a deep bruise. I have never seen anything like this before. Has this happened to anyone with their fish? I am curious and to prevent this occurance in the future. Any suggestions would be appreciated.