Swimming difficulty is a symptom of several possible issues. It is actually quite rare as "swim bladder" itself. Internal protozoan, water issues (parameters (GH, KH, pH, temperature, and/or conditions such as ammonia/nitrite/nitrate), genetics can all include this symptom with or without other observable issues.
Consider all of these as best you can. Euthanization may or may not be warranted depending upon how bad it is.