Sounds like a brood pouch or swim bladder issue, is it a male what position does it float in
I had the same issue in the past and used a rubber tipped Bobby pin to open up his pouch and try to gently let some air out and it never came back;
If you try that method be sure to have a gentle firm grasp and let him wrap your pinky, and another important thing to note Is the brood pouch is a very obvious existent opening that is located below the anal fin, you do no need to apply any pressure or make amy incision to open it, it is already open your simply trying to move its edges to let air out
I almost considered giving my horsea surgery without knowing better until I looked at him and realized the open is quite large and already open