I've done it, we've always called it "fizzing." Most of the videos are with larger fish (bass) but the principle is the same. But when it's an appropriate treatment only when they are clearly having issues swimming (struggling to stay right side up, sinking uncontrollably). Any chance it's been overfed? I had a six line that would eat and eat and it's little belly would get hilariously huge. If it's not food related or swim bladder related, I don't have a good solution. Sounds like's it's not swim bladder related if it's swimming alright then hopefully it's just a glutton.