How do you heal a koi carps large open wound but its not an ulcer?

To heal a koi carp's large open wound that is not an ulcer, first, ensure the water quality is optimal, as clean water promotes healing. You can apply a topical antiseptic specifically designed for fish, such as iodine or a wound sealant, to the affected area. Additionally, consider using a salt bath to reduce stress and prevent infection, while keeping the fish in a quiet environment. Monitor the wound regularly for signs of improvement or infection.