I was sitting in the living room where my Discus tank is and all of a sudden, little Casper started to dart and jumped up so high that he hit the top of the tank. I jumped out of the chair to see what was wrong with him. he was all spastic... and shaky and then went right into the corner of the tank and stayed there. He is breathing heavy. Before this happened I noticed one of the other Discus ( Lucy Lemon) really chasing him around being aggressive. After about a half hour I took my magnifying glass and had a look at him. Under his mouth where his chin is, he has two large white spots that look swollen to me. I really think that when Lucy Lemon went after him, it may have butted Casper right into the heater in that corner. Or he ran into the heater trying to get away. The mark actually looks like a burn. Has anyone ever heard fish getting burned on these hot heaters? I don't know what to do for him poor guy.Lucy Lemon has really been aggressive lately to the other two small Discus in the tank, but not bothering the older larger ones. Are there any heaters out there that have some kind of safety net-type surrounding it so that the fish do not get burned?