Background

This fungal infection is very common and affects all types of feshwater fish, including goldfish. Causes can typically include:

• Slime coat damage cause by rough handling or physical damage that allows free floating fungal spores to reach the skin.
• Secondary infection following a different goldfish disease, like Ich, Finrot, or Ulcers.
• Water quality changes, including temperature increase. Outdoor pond goldfish are more likely to be attacked in the spring when there is a sudden rise in temperature.
• Large amounts of decaying organic matter, like dead fish or old food, will increase the likelyhood of an infection by increasing the number of fungal spores in the goldfish tank water. 

Diagnose

Symptoms of Cotton Wool will look like white, grey, or brown cotton wool patches on the goldfish's body and fines. Goldfish eggs are also prone to this fungus. 

Treatment

Treatment:Remove affected fish to hospital tank if possible. Swabbing fungus patch with iodine may be sufficient to cure problem. If not, EITHER treat with fungicidal medication (e.g Jungle Fungus Eliminator in US, Anti-Fungus Remedy in UK) OR a .3% salt solution.

Precautions:Salt and medications affect the cycle so monitoring water quality during treatment is essential. If left untreated, fungus can spread very quickly and kill the fish.