Water conditioner against bacterial infections (e.g. mouth and fin rot) Disinfects and supports recovery. Water conditioner for use in freshwater in case of typical bacterial disease such as Columnaris disease, fin rot, gill rot as well as infections by Aeromonas or Pseudomonas bacteria. The treatment can also be used in case of an infection by ectoparasites such as fish leeches, fish lice or parasitic crustaceans affecting the gills, as to prevent secondary infections at the injured skin spots.