one of my oscar out of two which is 3inch long is heabily breathing and became unactive, he havnt eaten for 2 days now while the other one is still active and normal running up to the glass when i come by, the water periameter is normal its just the two oscar in a 75 growout tank and i havnt move any of the decor. he just sit at the bottom working his mouth constantly and gills
This isn't a proper diagnosis. Aerobic and anaerobic bacteria are everywhere. He does not need to clean his filter unless it becomes clogged or the output flow weakening.