White Cottony Fluff in Aquariums: Causes and Treatment (2023)

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A few months ago a friend of mine woke up to find that his fish tank was covered in a fluffy, white, cotton-like substance. We both had no idea what it was.

Over time we delved deeper and found several possible causes of this problem.

To save you a lot of time and hassle, I decided to write this article collecting everything you need to know in one place.

What is the cottony fluff in my aquarium?

The white, cotton-like fuzz in aquariums could be caused by fungi or white hair algae, but it could also be Saprolegnia or Columnaris, which are less common.

If you've found a cotton-like fuzz in your aquarium, here's what you should know:

1. Mushroom (very likely)

White Cottony Fluff in Aquariums: Causes and Treatment (1)

People use the terms fungus and mold interchangeably. "Water mold" is a broad term that includes over 200 species.

But many people classify water mold as a category of fungi. Your approach to this organism will not change, no matter what you call it.

The factors that distinguish "White Fungus" from "White Mold" are irrelevant to the average aquarist.

But if you have flaky white substances in the tank that resemble cotton, you are more likely to be talking about white mold.

The fuzzy white tufts in your tank could be fungal filaments formed as organic material breaks down. They thrive in environments with large amounts of waste.

(Video) Aquatasy - The Fungus Among Us - What To Do If You Have White Fungus Growing On Your Aquarium Wood

2. Algae (quite likely)

White Cottony Fluff in Aquariums: Causes and Treatment (2)

Like "fungus" and "mold," people use the terms "algae" and "fungus" interchangeably in reference to the white substances they have observed in the water.

The confusion makes sense because white algae have a fuzzy appearance, and many aquarists use terms like "cotton growth" to describe the organism.

But with algae, a closer look shows asmooth film that is stringierand not quite as fluffy as water mold.

If you have staghorn algae, it won't spread as quickly as white fungus, despite the many physical similarities between the two entities.

Coral algae in saltwater aquariums can turn white if exposed to the wrong pH and temperature.

However, coralline algae are a crusty coating on live rock. You would never confuse them with white mold.

3. Saprolegnia (not likely)

White mold (or white fungus) is not a threat to your fish. You can ignore these organisms if your tank has no fish.

Their presence is only problematic in a populated aquarium because it indicates poor water quality.

But what about those fuzzy spots you see on fish? Are they a cause for concern?

A study in aquaculture and fisheries (Xianle Yang, Siya Liu, Mao Lin, Renjian Ou, Pengpeng Song, Jiming Ruan, Kun Hu) analyzed Saprolegnia strains among freshwater fish in southern China.[1]

They described Saprolegnia as a filamentous fungal infection responsible for heavy losses in fish farms.

In other words, this particular strain of white mold should have you worried. Look for blurry white, gray, green, red, or brown spots on the fish.

(Video) How to Get Rid of White Fungus in Aquarium

While healthy fish can survive in tanks with Saprolegnia, factors such as poor water quality and improper parameters can weaken a fish's immunity.

This leaves the creature vulnerable to the destructive effects of Saprolegnia. Ask a veterinarian to recommend medicated food.

However, they should only make this recommendation after taking a mucus sample from the fish to identify the pathogen. This will confirm your diagnosis.

4. Columnaris (not likely)

Columnaris is not Saprolegnia. But hobbyists always confuse the two because columnaris can produce white, raised spots on the diseased fish.

For this reason, aquarists call columnaris “cotton disease”.[2]But columnaris is not a fungal infection. It comes from bacteria.

Other symptoms include lethargy, loss of appetite, and irregular swimming. Do not attribute these symptoms to white mold or fungus.

Again, you should consult a veterinarian. You can get clarity by sedating the fish and doing a small biopsy to prove your fish has columnaris as opposed to fungal infections like saprolegnia.

Once the vet has identified the strain, they can recommend effective treatments. In severe cases, the expert may recommend euthanasia.

How did my aquarium get this substance?

Saprolegnia, fungi, columnaris and algae usually proliferate in aquariums because you have used the following factors to create a favorable environment for the organism:

1. While cycling

A fluffy white material may appear during the cycling process due to the high levels of ammonia and nitrite.

Ofintroduce ammoniaand nitritesB. by adding fish or waste, a tactic that benefits the substance because it encourages the proliferation of vital nutrients.

The goal of the cycling process is to feed nitrifying bacteria and, in some situations, fungi and bacteriaAlgae can occurto crowd out the beneficial bacteria.

(Video) Aquarium, white fungus, white algae, and "clear slime"

But eventually the substance will fade as the bacteria multiply. You don't expect white fungus or algae to persist in a fully cycled aquarium.

White Cottony Fluff in Aquariums: Causes and Treatment (3)

2. Plants and ornaments

Plants and ornaments play two important roles in this situation.[3]

First, some decorations are already affected by white mold.Amateurs can ignore these fuzzy organisms because they don't know any better.

Therefore, these objects will introduce white fungus into the tank as soon as you put them in the water. Second, mushrooms don't thrive in a well-maintained tank.

But you can reverse the results of your strict grooming routine by adding plants and decorations with decomposing organic matter.

Mushrooms will grow on these items because they are rich in nutrients.But the fungi will eventually exhaust their new found food.At that point they will fade.

3. Fish waste and overfeeding

Waste and leftovers accumulate in a neglected tank, creating nutrients that encourage rapid fungal growth.

You can make this problem worse by overfeeding the fish.Overfeeding creates more fish waste and food waste. The fungus will grow all over this decomposing waste.

4. Elevated toxins (nitrogenous compounds)

Fungi and algae also thrive in the presence of nitrogenous compounds, including ammonia, nitrite, and even nitrate.

People associate high levels of ammonia, nitrite, and nitrate with rotting fish waste and debris.

But you can introduce these toxins into your aquarium during a water change ifYour supply is contaminated.

5. Poor circulation

Standing water not only leads to a lack of oxygen, but also allows fungi and algae to thrive. Weak filters create dead zones in the aquarium.

(Video) How to: Fix Mysterious White Flakes In Aquarium

Also, tanks without ventilation suffer from carbon dioxide accumulation.

And when you mix it with excessive light exposure, you almost guarantee algae and mold growth.

Where are fungi and algae usually found?

Mold and algae will grow on every surface in the tank including rocks, filters, hoses, ornaments and more.

But again, unless you have fish, white fungus or seaweed is nothing to worry about.

Fungus vs. White Algae: How Do I Tell the Difference?

Because mold is a type of fungus, it has many characteristics that people associate with fungi, including a fluffy, fluffy, cottony appearance.

In contrast to white algae, however, it is less stringy.Mold thrives in environments with adequate nutrients such as phosphates and nitrates.

White Cottony Fluff in Aquariums: Causes and Treatment (4)

how to remove it

If you want to get rid of the white, cottony fuzz in your tank, it doesn't matter if it's mold or algae.

Since both thrive in similar environments, the steps you need to take in both cases are the same:

  1. Manually remove the fuzzy growths. Be sure to wear gloves.
  2. Perform a partial water change. Depending on the health of your fish and the severity of the infestation, you can also do a 95 percent water change.
  3. Remove dead organic matter before it rots. Everything you can catch with your eyes must be removed, including dead fish.
  4. Install pump and air stones to improve aeration.
  5. Don't overfeed your fish. If necessary, use an automatic feeder. Fish should only eat twice a day for a few minutes at a time.
  6. Use a vacuum to remove debris from the substrate. I personally recommend thoseHygger aquarium gravel cleaner (link to Amazon).
  7. Add fish that eat white fungi and algae, such as plecos, mollys, siamalgae, etc. Here are mine32 best and worst algae eaters.

If you haven't already, I highly recommend testing your water for ammonia, nitrite, and nitrite at least once a week.

I personally do that with thatAPI FRESHWATER MASTER TEST KIT (Link zu Amazon), mainly because I found it to be the most accurate.

  • For a better visual understanding of the steps above, here's an excellent YouTube video showing how to get rid of the white stuff:

If you found this article helpful, you might also be interested in these:

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The white fuzz in your aquarium is probably a fungus or alga. Fortunately, if you want to get rid of it, it doesn't matter what it is.

In both cases the material can at least partially be removed manually. The next step will be to do a partial water change and test for nitrogenous toxins.

Regular maintenance is also essential as it prevents rotted debris from contaminating your water. Do not skip vacuuming the substrate.


  1. https://www.sciencedirect.com/science/article/pii/S2468550X17301697#bib10
  2. https://www.thesprucepets.com/how-to-treat-cotton-wool-disease-in-freshwater-fish-5075288
  3. https://aquanswers.com/white-fuzzy-stuff-in-fish-tank/


Why does my fish have white fuzzy stuff on it? ›

Fungal infections are one of the most common disorders for fish. Fungal spores naturally populate fish tanks, but sick, stressed or injured fish can cause a dangerous increase. These infections manifest as a white cotton-wool-like growth on the skin, mouth, fins or gills.

How do you treat cotton wool disease? ›

Treatment for cotton wool disease in freshwater fish includes salt baths using Freshwater Aquarium Salt or commercially available antifungal treatments for aquarium use. In some instances, the entire tank is treated, but if individual infections are present, treating the fish in a separate hospital tank is preferable.

What is white cotton wool in fish tank? ›

Cotton fin fungus is a condition that typically affects aquarium fish with weak immune systems. The condition also goes by the name “Cotton Wool Disease”, characterized by the cotton wool growths on different parts of the affected fish.

What eats white hair algae? ›

Algae with softer filaments are eaten by invertebrates like Amano shrimp and most dwarf shrimp species. Even snails like the highly popular ramshorn snails will go after the filamentous hair algae coats.

How do you treat cotton mouth in fish? ›

A medicated fish bath (ideally using aquarium merbromin, alternately methylene blue, or potassium permanganate and salt), is generally a first step, as well lowering the aquarium temperature to 75 °F (24 °C) is a must, since columnaris is much more virulent at higher temperatures, especially 85–90 °F.

What are the symptoms of cotton wool disease in fish? ›

A microscopic exam is required to tell the difference between fungus and Columnaris. Clinical signs include white, pale or greenish patches on the skin, fins and mouth. Severe infections can affect gill tissue and cause lethargic, loss of equilibrium and sudden death.

What fungicide does cotton use? ›

Proline. Bayer Proline is a powerful, broad-spectrum fungicide that provides disease protection for cotton crops and peanuts.

What causes cotton wool disease in fish? ›

Cotton wool disease is caused by the bacteria Flavobacterium columnare. It is not a fungus, despite its fungus-like appearance. It can infect the skin and gills and is of great importance to the commercial aquaculture market.

How do you remove fuzz from algae? ›

As fuzz algae attach themselves to the substrate very stubbornly, they are difficult to remove manually. Those that grow on the aquarium glass can easily be scraped off with a blade cleaner. When the aquarium is severely infested with fuzz algae, treat with Easy Carbo, combined with a sufficient number of shrimp.

What is the best way to get rid of hair algae? ›

How To Get Rid Of It (7 Ways)
  1. Improve Your Source Water. Your water makes your aquarium. ...
  2. Improve Your Water Parameters. Using RO or RODI water isn't always necessary. ...
  3. Manual Removal. ...
  4. Grow More Plants. ...
  5. Improve And Stabilize Your CO2 Levels. ...
  6. Chemical Treatments. ...
  7. Use Fish And Inverts To Remove It.
Feb 7, 2023

How does hydrogen peroxide treat hair algae? ›

If you are using 35%, the suggested dose is 1 ml per 10 gallons of water. I was using 12%, so I was doing 2 ml per 10 gallons. Turn off all flow in the tank, fill the plastic syringe with the food grade Hydrogen Peroxide shot a small amount of the Hydrogen Peroxide at the hair algae.

Does cotton mouth ever go away? ›

When the treatment stops, dry mouth usually goes away. Conditions that affect the salivary glands and cause dry mouth, such as Sjögren's syndrome, are usually lifelong. Everyone's mouth can be dry sometimes. If you feel like your mouth is always dry, it may be time to seek treatment.

Is Melafix good for cottonmouth? ›

Melafix is used by hobby fishkeepers to treat and prevent bacterial fish disease, including fin rot and cottonmouth disease. It is an option for those who prefer to use natural remedies on their tank.

What are the symptoms of bacterial blight of cotton? ›

Symptoms. The bacteria can affect the cotton plant during all growth stages, infecting stems, leaves, bracts and bolls. It causes seedling blight, leaf spot, blackarm (on stem and petioles), black vein and boll rot. On cotyledons small, green, water-soaked rounded (or irregular) spots form which turn brown.

What is the most common cause of cotton wool spots? ›

Cotton wool spots are believed to occur secondary to ischemia from retinal arteriole obstruction. It is thought to represent nerve fiber layer infarct and pre-capillary arteriolar occlusion.

What causes cotton disease? ›

Verticillium wilt of cotton disease is caused by Verticillium dahlia fungus. Reduced leaf size with mottling with yellow areas between veins and on margins; Brown necrotic leaves become dry and finally shed off.

Which is best insecticide for cotton? ›

Armigera and other bollworms. 4. Minimum foliar sprays of neonicotinoid insecticides such as Acetamiprid, Imidacloprid, Clothianidin and Thiomethoxam which are likely to aggravate insect resistance, since Bt cotton hybrid cotton seeds are treated with neonicotinoids. 5.

Is vinegar a fungicide? ›

Vinegar has antifungal and antibacterial properties, and it can be a cheap and effective treatment for many types of mold. Household white vinegar typically contains about 5 to 8 percent acetic acid.

What is cotton treated with? ›

Conventional scouring of cotton fabric involves a high-temperature treatment with a solution containing alkali, wetting agent, and detergent (Choudhury, 2006, p. 179). A chelating agent is often added to the scouring solution to complex any heavy metals present in the cotton.

What fungus looks like wool or cotton? ›

Chaetomium is the mold that you may have seen that looks like a white cotton-candy material. It is fluffy and can grow quickly.

Can cotton wool cause infection? ›

This study implicates a contaminated ball of cotton wool as a source of transmission of HCV and supports reports of iatrogenic causes as the main source of transmission of blood borne viruses in most developing countries.

What diseases cause cotton wool spots? ›

Diabetes mellitus and systemic hypertension are by far the most common etiologies of cotton-wool spots, followed by undiagnosed diabetes and hypertension.

How long does it take for a cotton wool spot to resolve? ›

Cotton wool spots classically disappear in 6–12 weeks, however in diabetic retinopathy they may persist for longer.

Can cotton wool spots be treated? ›

What treatment is available? Although there is no specific treatment for cotton-wool spots, treatment is directed toward any underlying conditions that caused the cotton-wool spots to appear. The spots themselves fade away over several months' time.

What do cotton wool spots look like? ›

Cotton wool spots present as opaque fluffy white spots, sometimes with feather-like edges, on the retina when seen on a funduscopic exam. These opaque white areas are typically asymptomatic, but may cause some vision loss due to the underlying disease state.

Are cotton wool spots serious? ›

Cotton-wool spots are tiny white areas on the retina, the layer of light-sensing cells lining the back of the eye. Caused by a lack of blood flow to the small retinal blood vessels, they usually disappear without treatment and do not threaten vision. They can, however, be an indication of a serious medical condition.

Does cotton wool shrink in water? ›

Sufficient volume of air is present in a limp of cotton wool. When dipped in water, this air goes out due to which the cotton lump gets shrunk.

What is cotton wool appearance differential diagnosis? ›

The cotton wool appearance is a plain film sign of Paget disease and results from thickened, disorganized trabeculae which lead to areas of sclerosis in a previously lucent area of bone, typically the skull. These sclerotic patches are poorly defined and fluffy.

What does a lump of cotton wool? ›

Lump of cotton wool has air among gaps of cotton fibres. When water replaces the air from these gaps, the cotton lump becomes heavy and also shrinks due to removal of air gaps. This is a physical change.

What does wool fungus look like? ›

The skin is initially thick, red, and “weeping,” and later, there is the appearance of crusty and scaly skin, and usually in circular lesions. Sometimes the wool appears “clumped,” as well. Hairs break easily and are usually lost beginning in the center of the lesion.

What is a cottonwool spot? ›

Cotton-wool spots (CWSs) are common retinal manifestations of many diseases including diabetes mellitus, systemic hypertension, and acquired immunodeficiency syndrome. Clinically they appear as whitish, fluffy patches on the retina and eventually fade with time.

What is the difference between hard exudates and cotton-wool spots? ›

Cotton wool spots (CWS) or soft exudates are small, light yellowish-white or grayish-white slightly higher lesions which appears as clouds on retina and their edges are blurry and not clearly defined. The hard exudates are small white or yellowish white deposits and their edges are clear and sharp.

What is cotton like fungus? ›

Cottony rot, also called Sclerotinia rot or white mold, affects many kinds of plants. It is also a disease of vegetables, such as beans, carrots, celery, and lettuce. Moisture and high humidity are necessary for development of the disease and this is one reason the disease is found lower in the plant canopy.

What are cotton wool exudates? ›

A cotton-wool spot, or soft exudate, is a yellow-white lesion in the superficial retina that usually occupies an area less than one fourth that of the optic disc (Fig. 69-19). A cotton-wool spot can occur singly or in conjunction with many others (Fig. 69-20).

How can you tell the difference between cotton and wool fibre? ›

Wool is an animal fibre, whereas, cotton is a plant fibre. Cotton is wrinkle resistant, whereas wool is not.

Does cotton wool rot? ›

Cotton wool is biodegradable, but the arguments against biodegradation are way too many and need to be carefully looked at. Well, cotton wool from 100% organic cotton can biodegrade safely and is okay for the environment.

What causes Roth spots? ›

Roth spots are most commonly associated with infective endocarditis and have been detected in 80 percent of cases of subacute bacterial endocarditis. They are also seen in association with conditions including leukemia, anemia, hypertensive retinopathy, preeclampsia, diabetic retinopathy, and anoxia.


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