What Can Cause White Fungus in the Fish Tank?

Fungal infections are common in fish tanks, and there’s no reason to be alarmed when you notice white fungus in fish tank. Though, they can colonize and spread rapidly. If your fish have been healthy all along and show premature signs of infection, it’s probably because of the poor water quality. 

Most fish-lovers quickly identify fungal infections in their fish tanks because of the fungus’ peculiar, white, fluffy appearance, known as the ‘cotton wool infection’. As the fungal infection becomes severe, the white changes to a dark gray or red if left untreated. 

Fish Tank

The Common Causes of Fungus in Fish Tanks

Fungus is common in all aquariums, though the severity can get aggravated due to certain conditions like:

  • Deteriorating water quality
  • Poor hygienic standards
  • Leaving dead fish in the tank for too long
  • Other decomposing matter present in the fish tank
  • Old, injured fish with other pre-existing diseases

If you notice recurring fungal infections, please check your aquarium for tank hygiene. Also, check if the filtration system is working correctly. If it is a chemical filtration system, it is advisable to suspend the filtration system temporarily until the infection is treated. It is crucial to maintain the water quality in a fish tank because healthy tanks with clean water rarely witness fungal infections. 

What Causes White Fungus Infection?

Usually, white fungus in the fish tank will break out when there’s much breeding activity amongst the fish. The eggs get infected with a fungal infection that turns white and fluffy. The species of Fungi responsible for spreading this type of fungal infection are Saprolegnia and Achlya. The condition, known as Saprolegniasis, is typical, with white patches appearing on the tissues of the fish infected with this fungus. 

Identify These Tell-Tale Signs

The tell-tale signs of this infection include hemorrhagic ulceration, skin erosion, etc. The fins, muscles, and gills of your pet fish also appear eroded. This type of fungus infection often infects infertile eggs and spreads to fertile eggs as well. It is advisable to remove all the infected eggs using a pipette or long forceps as these eggs cannot be treated or cured. Your pet fish may be down with liver mycosis, which may extend to the eyes, kidney, and spleen. If left untreated, your fish are likely to die due to the infection. 

One reason vets attribute to the breakout of this fungal infection is low water temperature.  The recommended water temperature for fish tanks is between 70 to 80°F. Hence, if the room temperature is likely to drop below 70°F, please ensure that the heater is on all the time to prevent white fungus infection.  

It is easy to determine if your pet fish is infected with white fungus. You may notice the typical cotton-like growth near the mouth and fins, and the fish may not be active and displays listlessness all day long. 

Your pet fish may not be swimming with the usual energy and may keep rising to the water surface or tend to take frequent rest breaks at the bottom of the fish tank. If you notice such peculiar behavior, it is advisable to consult your vet and have your pet fish treated immediately. 

Summing it Up

White fungus infection amongst most pet fish is quite common and can spread to all the fish in the aquarium if left untreated. Ideal tank temperature, and hygiene, are crucial for preventing such infections.


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