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Why does brown algae keep returning to my fish tank decorations?

Updated On September 23rd, 2025

Pet's info: Fish | Unknown - Fish

My fish tank is getting brown on the decorations and gravel I tried cleaning it a couple days ago but came right back

2 Answers

Most Helpful Answer

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Answered By Angel Alvarado, LVT

Licensed Veterinary Technician

Published on January 14th, 2018

Brown algae overgrowth can be due to high nitrates, too much light or overfeeding. Use a liquid home test kit or submit a water sample for testing. Most pet or fish stores will do this for free of for a small fee. If nitrates are over 40ppm, it can be decreased by performing partial water changes. Use only aged or conditioned water that is temperature matched to prevent stress or shock. You can also use a nitrate absorbing filter insert. The algae will need to be physically scrubbed from plants or rocks and can be scraped from glass. Rinse filter media using tank water NOT tap water. Limit light to 6 hours daily, 8 if you have live plants and do not over feed.

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    Answered By Angel Alvarado, LVT

    Licensed Veterinary Technician

    Published on January 28th, 2020

    Its the amount of light that can promote algae overgrowth. Limit lighting to 6-8 hours daily. Monitor water temp as well. Do not overfeed and remove dead/dying plant matter to also limit algae. You can remove any tank furniture and scrub them clean.

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