Whether you need to change the water after a goldfish dies depends on the specific circumstances.
Observe Water Quality Changes: If the goldfish has been dead for a short time and the water is still clear and unpolluted, you don't need to change all the water. At this point, the water quality has not deteriorated significantly and has no negative impact on the living environment of other fish. However, if the water quality gradually changes and shows signs of pollution after the fish dies, you need to change the water in a timely manner.
Determine the Cause of Death: If the goldfish died from saprolegniasis or other bacterial - infected diseases, then water change and disinfection are necessary. If the cause of death is temperature, lack of oxygen, or other objective factors, you also need to change the water in the fish tank promptly.
Handle the Dead Fish: After discovering a dead goldfish, you should remove it from the water in a timely manner to prevent the body from rotting and generating bacteria in the water. If the dead fish has rotted and polluted the water quality, you need to change the water immediately and carry out disinfection treatment.
Water Quality Management: Regularly check the water quality to ensure it is clean and avoid excessive levels of harmful substances such as ammonia - nitrogen and nitrite. Excessive amounts of these substances can cause health problems or even death in fish.
Water - changing Suggestions: If water change is necessary, it is recommended to change part of the water rather than all of it. Generally, changing one - third to half of the water volume is advisable to avoid discomfort in fish caused by drastic water quality changes.