Goldfish's tail turn black generally. There are many reasons for their tail turn black, such as common trauma, shock and other diseases. As long as the surrounding environment is kept stable and quiet, they can return to normal. Moreover, diseases like trauma or shock generally do not need drugs to treat them, so the recovery speed is also very fast. However, the tail turns black due to bacterial infection and vertical scale disease, and the breeder needs treatment before it can return to normal. If breeders can't treat them in time, they may not recover.

1. Stable environment: If breeders want to restore the tail of goldfish to normal, they must keep their living environment comfortable. If conditions permit, it is best to install a heating rod to keep the water temperature in a stable range. A filter should also be installed to slow down the deterioration of water quality.

2. Change water in time: Breeders should change water for them regularly to keep the water quality clean. Before changing water, it is best to expose the water to the sun for 1-2 days, so as to eliminate chlorine in the water.

3, drugging: Breeders can also wash their tails with yellow powder for 1-2 weeks continuously to avoid bacterial infection. Some crude salt should be added to the water where they live to inhibit the growth of bacteria. Finally, feed them more high-protein foods to speed up their recovery.