Weird Oscar Activity

I have an albino oscar about two years old. The past couple of weeks he has been lying at the bottom of the tank, breathing slow, and periodically swimming around. He has a loss of apatite and his tailfin quivers perionically. He is in a 100 gallon tank with a 15 inch African Knife fish, a 6 inch Pacus, a 12 inch pleco, and a 5 inch Tinfoil Barb. He was usually an agressive fish but he drasticly calmed down and developed some dark coloration in his fins. I have tried feeding him some greens with no luck. It doesn't appear that he is getting any pits in his head or lateral lines, any suggestions?