is a general name for fungal infections that are present in aquariums and feeds upon dead organic matter. Healthy fish protect themselves from fungal infections by producing mucous layers. When this is disrupted, fish can become infected with fungus.
Cotton Wool can be caused by: Any previous infections, parasites or injuries(Ich, Finrot, Ulcers) Rough handling and physical injury can damage the slime coat
Water quality changes that also include temperature increase. Outdoor goldfish ponds can suffer from sudden rise of temperature (in Spring)
Organic matter, uneaten food can increase the likelihood of an infection
What are the symptoms; A cotton wool like growth of fine, white strands is the most obvious symptom. There can also be grey or brown wool patches on the goldfish's body, fins and mouth.
How to cure Cotton Wool; Treatment can be relatively easy if done with anti fungal agents or salt baths. Treating the sick fish in a separate hospital tank is preferable. One tablespoon per gallon of water can be used when doing salt baths. Very common treatment includes Malachite Green.
How to prevent Cotton Wool; Maintain a high quality water, doing regular water changes, remove uneaten food or any dead material. Keep a close watch for any wounds or infection.
Rule of thumb: clean, healthy and well oxygenated water combined with a constant water temperature keeps your fish far away from diseases or problems.