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. The right side of it's face was noticeably darker. Within 2 days it turned completely black and it passed away. Has this ever happened to anyone else? I have never seen anything like this before. What do you think caused it? It may have bumped into this large rock I have in the tank. This is the only thing which could have caused it's death.
