I had an albino bristlenose catfish for more that 2 years maybe three. He was about 4 inches and he just died. when I found his dead body there were brownish green spots on parts of him. I think he died because I just got three new discus which I feed beefheart, mysis shrimp and freezedried tubifex worms and he started eating leftover discus food. Is this what killed him or was he just old?