Solutions to the problem of large areas of koi losing scales and exposing flesh:

1. Change the water of the sick fish first to avoid bacterial reinfection. Then use nitrofuracil powder to take a medicated bath on the sick fish. Take a medicated bath for 15-20 minutes every day for about 3 days, and the rotten parts will be improved.

2. Clean the exposed area first, and then apply potassium permanganate once a day for about a week. The exposed area will show signs of healing.

3. Transfer the sick fish to a separate container, and then sprinkle gallnuts directly into the fish tank. During the treatment period, it is best to change the water every two days. You can add the same amount of medicine every time you change the water, and wait about a week for the koi to recover.

The reasons why koi fish lose their scales and expose their flesh in large areas:

1. The reason why koi fish lose their scales and expose their flesh in a large area may be due to infection after trauma. Generally, it is Trauma occurs during fishing or transportation, or trauma caused by other sharp decorations in the water.

2. Large areas of koi scales falling off and exposing flesh may also be caused by bacterial infection. This situation is mainly due to poor water quality or unclean food.

3. Koi that have lost scales and exposed flesh in large areas may be suffering from red skin disease, because they are infected with parasites and bacteria at the same time. This situation is more likely to occur in spring and autumn.