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What's the white cotton stuff in my fish tank and how do I remove it?

Updated on September 23rd, 2025

My new fish tank is being occupied by some white cotton web like thing at the bottom.. the are found on the natural plants and food remainings in the tank.. please help .. how to get rid of it? I tried changing the water 3 times..

3 Answers

Most Helpful Answer

Answered By Todd Cecil

Veterinarian

Published on November 14th, 2018

Thanks for reaching out. This problem is perplexing, but possibilities include fungal or bacterial overgrowths. A good cleaning might help to alleviate your problems. Continue to test water quality and correct problems. Sometimes the over-growth of anaerobic bacteria (those which grow in low or no oxygen conditions, at the bottom of the tank), can form strange formations of detritus. Submitting a sample to a lab might help determine an answer.
Good luck.

1Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By Angel Alvarado, LVT
Licensed Veterinary Technician
Published on November 21st, 2017
By your description, it could be a fungal infection. This can occur with poor water quality or stress. It can also be introduced I to a tank by new additions.
Treatment is relatively simple and involves providing adequate water quality. Rinse filter media with tank water, not tap water, and perform a partial water change. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Common antifungal medications include Malachite Green, Jungle Labs Fungus Eliminator, Anti-Fungus Remedy (Interpet) or PimaFix (API). You can purchase these products at your local pet or fish store. Follow label directions.
If just the one fish is affected, consider separating it and treating it in a hospital tank. Return it to the main tank once treatment is complete.
1Pet Parents found this answer helpful
Answered By Todd Cecil
Veterinarian
Published on January 21st, 2020
Thanks for reaching out about Ares and including photos. White cottony growths are often associated with fungal infections, which are normally secondary to other problems. Wounds, suboptimal water quality and parasites could be the initial cause. Test and correct water quality. A veterinary visit is recommended to assess and provide a diagnostic/treatment plan. There are commercially available fungal treatment available but use with caution, especially without getting a confirmed diagnosis first. If aggression from other fish suspected, might need to be separated.
Good luck.
1Pet Parents found this answer helpful

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