It is not that bad. He has a bruise and a small piece of peeling skin. I was gone for a couple hours today. When i came back the nozzle on my emperor 400 was knocked off. the filter was not broken i just have to slide the nozzle back in. I am just worried that he will seriously hurt himself someday. he does stuff like this a lot. The tank is a 75 gallon 4ft tank. Why does he do this and what should i do to prevent this. It is not that bad. he always does stuff like this and it heals in a few days. i just wanted to stop it.