How do you fix a koi swim bladder?
As a short term relief for fish with swim bladder issues, it is commonly suggested to put them in a warm, dark, shallow bath of water containing salt or Epsom salts (3g per L for long terms baths).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7692175/#:~:text=Disorders of the swim bladder,or floating on the surface.