Hi @TomK Nope, that is not fin rot. Did you move that fish recently or was there some reason the water he was in had different parameters? Maybe colder? Another possibility is fighting. Stress from fighting often leads to that. But not worry, if the tank water is good and he gets fed well he will recover in a couple of days. Not fin rot. Rgds Marco
Yip Marco, spot on. I had heater problems and the temp yoyo'ed a lot. I was suspecting that that could have something to do with it. Thanks