There are three reasons for the congestion of koi fish tail, the first is collision with hard objects, the second is infection with germs, and the third is stress reaction. Usually, don't put hard and sharp objects in fish tanks, otherwise it will do harm to fish. At ordinary times, we should pay attention to changing water and keep the water clean and hygienic, so as to avoid infection with germs. As for stress reaction, it is mostly related to inadequate feeding, so we should pay attention to controlling temperature and stabilizing water quality at ordinary times.

1. Change water in time: After finding congestion of fish tail, it must be changed. By changing water, the water quality can be improved, and some germs in the water can be discharged, thus avoiding further deterioration of the disease, which is very helpful for the recovery of fish. At this time, the water should be changed frequently, usually every other day.

2. Raise the temperature and lower the salt: In order to improve the resistance of fish, it is necessary to properly raise the water temperature, control the temperature between 20-25 ℃ and keep the constant temperature, so that the metabolism of fish is accelerated and it is helpful for it to discharge harmful substances. In addition, salt should be properly added, and the concentration is generally two thousandths.

3. Smear the diseased part: If the fish's condition is not very serious, it is not necessary to take a medicated bath, just smear the prepared medicine on the bleeding part, let it stand for 20 seconds after smearing, and then put it back in the fish tank.

4. Medicated bath treatment: If the condition is not optimistic, the fish should be treated with medicated bath. Prepare a fish tank, pour the water from the original tank into it, then add a little trichlorfon and yellow powder, and use an oxygen pump to oxygenate, put the sick fish into it, soak it for about 20 minutes, then fish out the clear water again and put it back into the fish tank.