Why does your goldfish have white fluffy stuff all over him?

Goldfish do not grow white, fluffy stuff all over them in healthy conditions. The most likely cause of white, fluffy stuff on a goldfish is a fungal infection. Fungal infections can occur for a variety of reasons, including poor water quality, stress, and injury. If you notice white, fluffy stuff on your goldfish, it is important to take action to treat the infection as soon as possible.