red belly pacu

pinkyshot

I have a red belly pacu who is about 5 months old, hes in a 75 gallon tank with a few other smaller fish, I notice yesterday he was not really eating his algae wafers that we drop in the water..he usually catch them as the float to the bottom, than today when i fed him he didnt eat any and I was looking at him and notice that his lower jaw looks to be swollen. I know he some times freaks in the tank and has hit the sides, and the top, for no reason sometimes.....I was wondering if anyone has heard of this hapenign to a fish...i did puy some rid-fungus treatment in there just in case...but if anyone knows what i should get i will go buy it. I did a water change and cleaned the bottom real well about a week and a half ago i do it about every 2 weeks. I have had this tank going for about 5-6 months and have had no prob with him getting hurt. could he have hurt it eating his wafers cause they are kind of hard its his favorite food. any help would be good, so that i can try and treat him.