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White Algae In Fish Tanks: Causes & Step-By-Step Solutions

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Many aquarists encounter what appears to be white algae in their fish tanks. However, finding this stuff immediately raises some questions.

Is this actually algae? And if so, what caused it and how am I supposed to get rid of it? These are the questions I have asked myself countless times in the past.

Therefore, to make it easier for you, I decided to collect all the essential information in one article. Let’s dive right into it.

How Do I Know If I Have White Algae In My Tank?

If the white substance is a fuzzy growth, you probably have fungi. Fungi are fluffy organisms. Unlike algae, they don’t contain chlorophyll or perform photosynthesis. 

In fact, fungi don’t need light to thrive. The detritus, leftovers, and fish waste provide sufficient nutrients for the organisms. 

Algae are unicellular or multicellular organisms that photosynthesize.[1] Look for a slick film comparable to a web as opposed to a fuzzy substance

Algae will cover plants, ornaments, rocks, and the like. If you have doubts, collect a sample and send it to a lab for analysis.

You can’t use their location to differentiate between algae and fungi. They will grow on the same objects in the aquarium.

Some people expect algae to bloom immediately on new plants and driftwood because of the detritus they shed. But the same can be said for fungus.

While you are better off classifying all white fuzzy growths as fungi, a lab analysis will provide definitive results.

While algae are filamentous and look like thin films, fungi appear as cotton-like growths.

What Causes White Algae?

White alga appears in poorly maintained tanks, especially when it persists. Consider the following:

1. Aquarium Cycling

Cycling boosts your tank’s biological filtration by introducing nitrifying bacterial colonies that turn ammonia into nitrates

Without these colonies, the ammonia will run amok, poisoning any aquatic creatures you introduce. 

Some people use fish to cycle tanks, but this practice is tricky and requires a skilled hand. 

Algae and the nitrifying cycle go hand in hand because this process introduces ammonia and nitrates to the water. 

Think of ammonia, nitrates, and nitrites as fertilizers for algae. Algae spores require ammonia to grow.[2]

Adult algae will use nitrates and phosphates to thrive. But algae in an aquarium are a positive sign. They show that your tank’s cycling process is almost over.

Once the tank stabilizes, and if you perform routine maintenance, the algae should disappear.

2. Fish Waste

Algae and nitrogenous waste are closely linked. 

In fact, a study in Frontiers in Bioengineering and Biotechnology analyzed methods of using algae’s appetite for nitrogenous waste to clean recirculating aquaculture systems.[3]

Nitrogenous waste generated by the cycling process is not a cause for concern because it eventually subsides. 

But the ammonia, nitrates, and nitrites originating from fish waste and leftovers are a different matter.

Even with a powerful filter, nitrogenous waste can still overrun your aquatic environment because tanks are closed systems. White algae will multiply in the process.

3. Light Exposure

As you now realize, algae boast many attributes people associate with plants. That includes algae’s dependence on light. 

A paper from the University of Kragujevac (Faculty of Science, Institute of Biology and Ecology) noted that algae’s growth in an aquarium was tied directly to the intensity of the lighting and duration of exposure.[4]

This is why professional aquarists are reluctant to leave their aquariums in direct sunlight. 

The UV rays will encourage the algae to outcompete the plants for nutrients, which you don’t want. 

4. High CO2 Levels

Algae has an interesting relationship with carbon dioxide. The common belief is that high CO2 levels boost algae growth.[5]

After all, like plants, algae take in CO2 and generate oxygen. But it isn’t that simple. White algae will appear because you have an imbalance in nutrients, CO2, and factors such as light. 

Sometimes, too much CO2 can inadvertently lead to rapid algae growth by increasing your plants’ nutrient uptake and creating an imbalance. 

White algae will appear because of a collection of factors, not just high or even low CO2 levels.

Are White Algae Bad For Fish?

White algae do not harm fish, not directly. Some people think white algae is dangerous because their fish died shortly after they noticed the algae. 

However, these organisms thrive in tanks with decaying organic matter.

In other words, your fish might have died because of the ammonia and nitrites from decomposing organic matter. 

Even with a colony of nitrifying bacteria in the tank, ammonia can still spike to dangerous levels if you fail to remove rotting waste. 

A paper in ‘Water, Air, and Soil Pollution’ (Dingxin Wu, Minling Cheng, Shumiao Zhao, Nan Peng) also noticed that harsh lighting and significant algae growth could limit the concentration of nitrifying bacteria.[6]

Don’t expect the biological filtration system to compensate for negligence. Don’t be so quick to blame your dead fish on white algae. 

Yes, it forms a slick web, but most fish can swim through it unless they are too small and weak from disease.

How Do I Remove White Algae From My Fish Tank?

Even though white algae don’t harm fish, you should remove them because the organisms are unsightly:

  • Start by cycling the tank to completion. This can take six or more weeks. 

You need nitrifying bacteria in the tank to control the nitrogenous waste, and their formation takes time.

Make sure you don’t wash the filter media with chlorinated water. Chlorine will undo the cycling process by killing the nitrifying bacteria.

If you don’t want to wait that long, you can use products like API QUICK START (link to Amazon), which already contains live nitrifying bacteria.

Just remember that it is not enough to add these spores. You will need to feed them ammonia, which you can also get online.

Your tank will be considered cycled when you see the ammonia levels gradually drop to 0 ppm and nitrate begins to form. You can add your fish at this point.

  • Perform weekly water changes (30 to 50 percent). The size of the water changes will depend on the concentration of waste. Dangerous levels of ammonia require more significant water changes.

Pro tip: If you suffer from frequent ammonia spikes, here is my complete guide on this topic, in which I explained why it happens and how to overcome it.

  • Use your hands or a net to fish dead organisms out of the water. Otherwise, they will raise the ammonia concentration once they rot.
  • Introduce more plants. You want the plants to starve the algae by consuming all the nutrients.
  • Don’t use the new plants as an excuse to overwhelm the tank with light. Maintain a regular day/night cycle. Don’t keep the lights on for longer than necessary. 
  • Install filters and pumps that produce proper agitation. You don’t want the water to become stagnant (or CO2 will spike).
  • Introduce creatures that eat white algae. That includes mollies, plecos, Amano shrimp, snails, etc. You can find my complete list here.

If these creatures won’t eat the algae, starve them for a few days to force their hand. 

Some tank cleaners will ignore the algae and detritus in the aquarium if you keep them well-fed. They need a reason to look for alternative food sources.

  • Scrape the algae off the surfaces in the aquarium with a toothbrush. Because the organisms form elaborate webs, you can pull them out with your hands
  • Apply anti-algae products that attack the white algae without harming the fish. Read the warning labels carefully. You don’t want to poison your fish accidentally.
Amazing YouTube video showing how to get rid of algae in home aquariums.

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White algae are usually filamentous and may resemble human hair. It’s a bit different from a fungus, which will have a more fuzzy appearance.

This substance is not dangerous, although it may indicate that something is wrong with the water. Start by testing for toxins like ammonia and nitrate.

If the way it looks bothers you, feel free to remove it. You can easily do this with your hands, just remember to wear gloves.