A rotten tail of a goldfish may be caused by changing the water too often, not changing the water in time, or poor water quality. It may also be caused by the goldfish contracting a bacterial disease. Parents should change the water reasonably when feeding goldfish to keep the water quality hygienic. Do a good job in water disinfection and maintain water temperature.

Tips:

The feeding density of goldfish should not be too dense. It is best to use 1 liter of water for 1cm goldfish.