The treatment methods for koi with flesh rot include the use of antibiotics, improving water quality, and isolated treatment, etc.

Using Antibiotics
Antibiotics can be used to treat koi with flesh rot. For example, drugs like aureomycin or tetracycline can be applied to the ulcerated parts of the koi's wounds. In addition, drugs such as furacilin, furazolidone, and malachite green can also be used for treatment.
Improving Water Quality
Koi with flesh rot may be caused by water quality problems. Therefore, improving water quality is an important measure in treating koi with flesh rot. Appropriate amount of salt can be added, and the water should be changed regularly to keep the water clean. Water conditioners can also be used to improve water quality.
Isolated Treatment
Isolating the sick koi for individual treatment can prevent the spread of the disease. During the isolated treatment period, special drugs can be used for treatment. For example, high-concentration potassium permanganate or chlorine dioxide can be used for medicated baths.
Precautions
During the treatment of koi with flesh rot, the following points need to be noted:
Keep the water temperature suitable. Usually, the treatment effect will be better when the water temperature is above 23°C.
When using drugs for treatment, pay attention to the dosage and frequency of drug use to avoid causing unnecessary harm to the koi.
Stop feeding during the treatment period to reduce the metabolic burden of the koi.
Maintain good water quality during the treatment process, which can be achieved by increasing the frequency of water changes and using filtration equipment.
In conclusion, the treatment methods for koi with flesh rot mainly include the use of antibiotics, improving water quality, and isolated treatment, etc. During the treatment process, it is also necessary to pay attention to maintaining good water quality, suitable water temperature, and the rational use of drugs.