The blackening of fish tail is due to the deterioration of water quality, the high content of ammonia nitrogen and nitrate in water, the inflammation of fish, and the congestion of tail capillaries, which leads to local blackening. In view of this situation, it is necessary to change water in time, improve the water environment and keep the water quality clean and sanitary, and it will recover slowly. In the daily feeding process, it should be changed regularly, about a quarter at a time.

1. Change water: After finding that the tail of fish turns black, the first thing to do is to change water, because the ammonia nitrogen content in the water is already very high at this time. If the water is not changed in time, the situation will continue to deteriorate and even lead to the death of fish. In order to improve the water quality as soon as possible, it is best to change it every other day, so that the water body will be clean and sanitary.

2. Heating up: What should be done after changing water is heating up. Heating up can promote the metabolism of fish and is of great help to its recovery. It should be noted that if the temperature rises too fast, the fish will feel uncomfortable, so it can only rise by 2 ℃ every day until the temperature is about 3-5 ℃ higher than usual.

3. Salting: Besides changing water and heating up, what needs to be done is to salt. Salt can change the osmotic pressure of water body, so as to prevent bacteria from invading, avoid infection with other diseases during treatment, and at the same time help its recovery.