I have a 129 gollon tank. Been set up for about 5 months now. Hob emporer 400 and a marineland c-530 can. Undergravel filter also. 1 common oscar, 2 tiger oscars and 1 albino oscar. Also a pleco. All fish are normal and acting great except 1. The common oscar is hiding, breathing heavy, not eating, has white poop hanging from him, a couple scales look to be falling off. Otherwise his fins and head look perfect. All my water tests are coming out great. Idk what to do? I've read so many things online but don't see it directly applying to his situation. I was feeding a mix of live roses and gold fish but stopped a few days ago after reading that they can get your fish sick! Please help!