White Stringy Film In Fish Tanks: Causes & Treatment

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It can be quite overwhelming to find your tank covered in a white stringy film that has suddenly appeared for no reason.

At least that was how I felt a few months ago when I had to deal with this issue. Since I had no idea what it was, I spent a few days researching.

To save you a lot of time and trouble, I decided to collect all the essential information I found into one article. Let’s dive right into it.

What Is The White Stringy Film In My Fish Tank?

After a ton of research, I found that there are three main causes for this substance:

  • Fungus
  • White Hair Algae
  • Hydra

Below is a brief explanation of each followed by instructions on how to get rid of it and prevent it from returning:

1. Fungus

Fungi are as commonplace in an aquarium as algae. Although aquarists associate fungi with a different brand of threats.

  • What Is Fungus?

Fungi are organisms that grow on decomposing matter. People confuse them with algae even though the two entities couldn’t be more different from one another. 

Algae are a form of plant matter, while fungi are parasitic organisms that grow on organic matter, such as feces and dead plants.[1]

When you leave a slice of bread on a table for several days, it develops fungus, not algae. 

Algae destabilize tanks by competing for nutrients with aquatic plants. They can also block a fish’s access to light and oxygen. Fungi are even more dangerous. 

A paper in the Pakistan Veterinary Journal (Zafar Iqbal, Rabia Mughal, Uzma Sheikh) blamed hemorrhages, fin and scale erosions, and belly distensions on fungal infections.[2]

This other study in the Veterinary Research Forum (Zahra Tulaby Dezfuly, Rahim Peyghan, Maryam Shokoohmand, Roya Rahnama) looked at Achyla infections in fish, specifically Oscars.[3]

The paper noted that harmless water molds (Achlya) could transform into pathogens under the wrong conditions (Poorly maintained tanks), threatening the well-being of fish in the process by suppressing their immunity.

While many fungi are white, they can also take on gray, yellow, and brown colors, depending on the species.

  • What Causes Fungus In Aquariums?

Vinay Verma (Feed and Fodder Technology Laboratory, Indian Veterinary Research Institute) studied fungal infections and diseases in fish.[4]

He blamed the proliferation of these illnesses on poor-quality water. 

Water quality deteriorates when aquarists neglect their maintenance routines. That includes forgetting to change the water and failing to remove rotting organic matter. 

Poor feeding habits can also exacerbate this issue. For instance, some aquarists overfeed their fish, unaware of the resulting increase in waste production and leftovers.

But you can overfeed your fish without attracting fungus if you maintain a rigorous maintenance routine. This is why professional aquarists blame fungal infections on poor maintenance. 

  • Where Is Fungus Usually Found?

Fungus grows on organic matter. The organisms will form distinct markings and patches on fish and plants.

You can also see it growing on driftwood and on the surface of the aquarium, although live creatures provide a better growing medium.

  • How To Identify Fungus?

If you can’t differentiate between white algae and white fungi, algae are almost always slimy, regardless of where you find them.

Fungi are dry and powdery, appearing in patches instead of clusters. You may also see white, thin stringy films hanging close to the surface.

If you have the time, you can also take a sample to a lab. Fungi have fine white threads (Hyphae). A lab test will identify these distinct features. 

  • How Do I Remove Fungus From My Fish Tank?
  1. Find the infected spots and rub the fungus. You can easily do this with a bucket full of water and a soft cloth.
  2. Perform weekly water changes of about 15 to 20 percent.
  3. Use water conditioners to combat high concentrations of ammonia and nitrate. I wrote everything there is to know about it here.
  4. Make sure the filter is not clogged.
  5. Remove dead plants and animals.
  6. Do not overfeed the fish – give them what they can eat in two to three minutes.
  7. Vacuum the substrate at least once a week. This is one of the most effective ways to prevent ammonia spikes.

2. Hair Algae

White hair algae in a planted tank.

Hair algae are a common problem in poorly maintained tanks. Fortunately, they are relatively easy to identify.

  • What Are Hair Algae?

Algae are photosynthetic organisms that may harm aquatic plants by consuming vital nutrients.

Hair algae have a filamentous structure. The length and arrangement of those filaments depend on the type of hair algae.

While hair algae are not inherently dangerous, they can become a nuisance by forming thick webs that trap fish.

They can also restrict access to sunlight, especially when you permit them to become incredibly dense. 

  • What Causes Hair Algae In Fish Tanks?
  1. You have too much waste. Algae thrive in the presence of high ammonia, nitrite, and nitrate levels. Hydrogenous waste becomes a problem when you allow fish waste, leftovers, and dead organisms to decompose.
  2. Overfeeding can increase hydrogen waste by elevating the volume of decomposing waste and leftovers.
  3. You can combat waste by performing water changes and cleaning the tank routinely. But if you neglect to perform these tasks, the algae will multiply until they destroy your aquarium.
  4. Phosphate levels are too high.
  5. The tank has poor circulation because of a weak filter (or maybe you don’t have a filter).
  6. Excess lighting encourages algae growth, as I discussed here.
  7. Crowded conditions allow hydrogenous waste to accumulate at a faster rate.
  • Where Are Algae Usually Found?

The algae attach to solid surfaces in the tank, including rocks, driftwood, ornaments, and plants.

  • How To Identify Algae?

Hair algae resemble hair. White hair algae are often compared to a slick film or a web.

The exact appearance depends on the type of algae. For instance, staghorn algae can take on a white color.

  • How Do I Get Rid Of Hair Algae?
  1. Introduce algae eaters (mollies, shrimp, snails, etc.). Here is my complete list of species that can take care of your problem.
  2. If the algae have grown in significant clusters, you can pull them out by hand or with a toothbrush, as I explained here.
  3. Perform regular water changes to prevent ammonia and nitrate spikes.
  4. If the ammonia is above 0 ppm or the nitrate is higher than 20 ppm, consider using a water conditioner.
  5. Remove waste and dead organisms before they decompose.
  6. Maintain a regular day/night cycle. Avoid prolonged or harsh lighting (no more than 8-10 hours a day).

Pro tip: If you suspect your tank has white algae, here’s an article I wrote with step-by-step instructions on how to get rid of it.

3. Hydra

The microscopic structure of hydra.

Hydras look like corals, anemones, and Jellyfish. 

A New York Times article in the Center for Biological Diversity classified them as truly immortal creatures that can live forever.[5]

But that doesn’t mean they are impossible to remove from an aquarium. 

  • What Is Hydra?

These polyps consist of a tubular body with tentacles on one end and a sticky foot on the other. They have an average length of 0.4 inches. 

The sticky foot attaches to a secure surface, and the tentacles use venom to paralyze whatever prey they catch.

The creatures eat tiny organisms, such as worms, water fleas, mites, and newly hatched shrimp, to mention but a few. 

Some aquarists use them to measure the aquarium’s health because they thrive in very clean water.

White hydras are called ‘Hydra Vulgaris.’ They may take on light brown and beige colors.[6]

  • What Causes Hydra To Form?

These creatures will hitch a ride into your tank on new plants, decorations, rocks, driftwood, and the like. 

  • Where Is It Usually Found?

Hydras usually occupy plants and the walls of the tank.

  • How Do I Identify Hydra?

At a distance, hydras resemble white specks on the glass walls of a tank. A closer look will reveal a tubular body and tentacles.

  • How Do I Get Rid Of Hydra?
  1. Soak infected plants and decorations in a bleach solution for 15 minutes (10 percent bleach). Don’t forget to rinse thoroughly afterward.
  2. Add creatures that eat hydras (mollies, gouramis, pond snails, etc.).
  3. Remove the tank’s inhabitants and raise the temperature to 104 degrees F or higher.
  4. Feed your fish sparingly.
  5. Apply salt treatments. Add 1 rounded tablespoon for every 5 gallons (20 L). You may use the API AQUARIUM SALT (link to Amazon) for this purpose.
  6. You may apply chemical treatments available on Amazon, but only after removing sensitive creatures such as snails.
Excellent YouTube video showing how to get rid of hydra in fish tanks.

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If you’ve found a stringy white film in your fish tank, it’s probably a fungus, algae, or hydra. Each one is different from the others, but luckily, it’s pretty easy to remove.

Fungus and white hair algae are quite similar to each other. Both look the same and grow on organic matter, including plants and driftwood.

You can use a cloth and scrub them pretty easily. Hydra is usually attached to the glass of the aquarium but it can also be removed.

After getting rid of them, you should check the water parameters, with ammonia and nitrate in particular. Algae and fungi thrive in the presence of these toxins.


  1. https://byjus.com/question-answer/what-is-the-difference-between-the-algae-and-fungi/
  2. https://www.researchgate.net/publication/262372880_Fungal_Infections_in_Some_Economically_Important_Freshwater_Fishes
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6522188/
  4. https://www.veterinaryworld.org/2008/February/Fungus%20disease%20in%20fish,%20diagnosis%20and%20treatment.pdf
  5. https://www.biologicaldiversity.org/news/center/articles/2012/new-york-times-11-28-2012.html
  6. https://www.garnelio.de/en/blog/aquarist-tips/hydra-or-freshwater-polyps-small-cnidarians-in-the-aquarium