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My goldfish has a fuzzy white growth. Is it fungus? How do I treat it?

Updated On September 23rd, 2025

I have two comet goldfish. I realized that one of them was turning a brownish-black color. After a bit of research I realized that the level of ammonia was to blame and so I did a 100 % water change. After the water was clean I saw that my other fish has a white streak that runs across his lower half. From the side it looks flat but from about it looks a bit fuzzy. It might be fungus but I'm not entirely sure. Can you help yo identify what it is and how to get rid of it? Please and Thank You

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3 Answers

Most Helpful Answer

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Answered By Angel Alvarado, LVT

Licensed Veterinary Technician

Published on August 29th, 2017

If it is fuzzy, it is likely fungal. You can try with a commercial antifungal medication such as API Fungal Cure, methylene blue or Pimafix/Melafix. These can be purchased online or in the aquarium section of most pet stores. Read package directions carefully and remove the carbon insert from the filter before treatment if indicated. Plain aquarium salt (NOT table salt) can be used in conjunction with one of the above treatments to aid healing. Dissolve up to one tablespoon per gallon of water into the tank. Fungal infections can take up to two weeks to resolve with treatment. Maintain proper water parameters (0 ppm ammonia/nitrites, 40ppm or less nitrates and temp of 65 F to 72 F). If possible, remove the affected fish yo a hospital tank during treatment.

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    Answered By Angel Alvarado, LVT

    Licensed Veterinary Technician

    Published on August 29th, 2017

    It may have been her slime coat coming off. The black color could have been caused by high ammonia levels. It can cause "burns" which will discolor scales. In the future, it is best to perform 30-50% water changes daily to balance chemistry and improve water quality. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Your filter should be rated to handle at least twice the water volume of the tank.

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    Answered By Angel Alvarado, LVT

    Licensed Veterinary Technician

    Published on September 16th, 2017

    Check the water temperature and chemistry. Goldfish do best in water between 65 F and 72 F. They make more waste than other fish, so require much better filtration. Without a filter in a properly cycled tank (bowl is not appropriate), ammonia and nitrites can become dangerously elevated. The stress can lead to infection. White fuzz can be fungal infection. White dots, like grains of salt, may be ich. He needs clean water at the appropriate temperature and medication. You can purchase medication to treat fungus or ich in your local Petco. Look in the aquarium section. Follow label directions carefully. Plain aquarium salt (NOT table salt) can be used to aid healing. Dissolve 1 teaspoon per gallon of water into some tank water and treat for 7-10 days. Partial water changes will be necessary afterwards to decrease salinity.

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