My 4 yr old oscar is bleeding from his gills when he attempts to eat. He seemed to be working his mouth afterwards the first time it happened 3 days ago. I thought maybe he had a piece of pellet lodged, so I did a wc and waited a few days to feed again. Well this time he did not even get a pellet and it was like the act of opening his mouth wide caused the discomfort and bleeding. He acted almost like he was gagging. Otherwise his behavior is ok and no visible abnormalities. Not sure what to do or what is wrong. Nitrate < 20, temp 76.6, ph 6.6.