What is the White Fuzzy Stuff in My Fish Tank? Mold or Algae?

what is the white fuzzy stuff in my fish tank

In the process of maintaining your aquarium, you may see white stuff growing in the fish tank and have no idea what it is.

The appearance of strange things in your aquarium is not always harmless. They can be the source of disease-causing your fish to die.

What is the white fuzzy stuff in my fish tank?

The white stuff growing in fish tank would commonly be referred to as the white algae. While the white cotton like stuff in fish tank is sure to be water molds.

Are water mold and white algae bad for fish? Let’s keep reading to know more!

What is the White Fuzzy Stuff in the Fish Tank?


Normally, the white stuff growing in fish tank is referred to as white algae. On the other hand, the white cotton-like stuff sticking on aquarium rocks is mostly water mold.

Both filaments and fungi can indeed appear white, but there are still some things you can see with your eyes to tell them apart.

1. Water mold

The white fuzz that quickly took over the bottom of your fish tank could be water mold. They grow at a much faster rate and look super fluffy.

Water mold (Saprolegniales) commonly lives on decaying organic matter. If present in your tank, they can sometimes cause diseases for fish and any aquarium plants.

In most cases, water mold results from the presence of leftovers and biological processes, including photosynthesis and metabolism. Water contamination and poor tank maintenance are also the main reasons for spreading of water mold.

2. White algae

Meanwhile, white algae don’t grow as fast as fungi. What more? White algae are not as “fluffy” as fungus; they look stringy and clearer.

Is It Harmful to Your Fish and Other Aquatic Inhabitants?

Most of the “white fuzz” stuff in your fish tank are water mold species. The water mold (Saprolegnia) generally isn’t harmful to your fish, but it’s not the case if there is too much mold on fish tank.

A large amount of white fungus can cause fungal infections in fish. You will start seeing white fuzzy patches on your fish’s body, mouth, and fins. In worst cases, Saprolegnia is a reason for eye infections and some digestion problems and gradually kills them.

The white fungus can be a threat to your fish, so you have to look for treatment immediately.

What Causes White Mold to Appear in My Aquarium?

White fuzz doesn’t appear for no reason. The main reason is supposedly due to the presence of three factors: fungi, bacteria, and parasites. Let’s take a look at the following common cause:

  • Fungal infection: Sometimes, fungal infection is the cause of white fuzz. This reason is less common, but it still can happen.
  • Leftovers food: Overfeeding can lead to leftovers in your fish tank. The water molds will take advantage of this food. They feast on and grow quickly. In addition, the excess food will rapidly decay and pollute the water, creating a perfect environment for white fuzz growth.
  • Poor aeration: Lack of aeration causes a low level of oxygen in the water, and the white film thing will start to grow.
  • Dirty driftwood: Without cleaning daily, your driftwood will get dirty, and the molds, bacteria, and fungi will stick to there and grow.
  • Suffering fish: An injured fish can be a perfect host for mold to grow and spread. So, in case you notice your fish has negative health symptoms, isolate and handle it as soon as possible.
  • Using untreated tap water: The chlorine in untreated tap water can kill beneficial bacteria in your aquarium that help the mold spread easier.

How to Get Rid of the Fuzzy Growth?


To treat white fuzz in fish tank, follow these tips below:

  • Figure out the hosts

The problem may start from a tropical fish hiding on the bottom of the fish tank or any decoration items. Try to find out and remove it immediately.

  • Not overfeed

Stop overfeeding your fish until you can remove all white fungus from your aquarium. Otherwise, the leftovers will become the nutrition for fungi and bacteria to spread.

  • Clean all decorations

The most important thing is to clean everything inside the tank thoroughly, as the white fuzz can even stick on aquarium rock.

  • Change water (50%- 95%)

Not all; depending on the size of your fish tank, you should change from 50%- 95% fresh, clean water.

  • Using non-chemical cleaner

Chemicals can be harmful to living creatures, it’s better to use non-chemical cleaners or natural products to clean water and remove white algae in fish tank. This is not only not harmful to the fish but can also limit new pathogens in the tank.


How much time does it take to remove white algae?

Chemical agents like bleach dips can help you get rid of white algae in aquarium in just 1-3 days, whereas it takes 2-3 weeks for harmless manual methods.

It is difficult to give a proper answer to this question because the time to get rid of white stringy algae depends on the method you use.

Are white algae dangerous for fish? While mold can be harmful, white algae don’t have any direct negative impact on fish and other aquarium inhabitants. This is also one of the differences between white algae vs white mold.

However, algae looks like white slime sticking on aquarium glass that makes your fish tank dirty, so you should not keep it.

Here are the three most popular ways to get rid of white algae in your aquarium:

  • Using bleach
  • Using a toothbrush
  • Using an aquarium scraper
  • Keeping algae eaters

What fish will eat white algae?

Algae eaters can help remove white hair algae aquarium. Here are some algae-eating fish you can consider keeping in your aquarium.

  • Siamese algae eater
  • Otocinclus Catfish
  • Bristlenose Plecostomus
  • Mollies
  • Hillstream Loach
  • Bristlenose Plecos
  • Chinese algae eater
  • Twig Catfish

Do white algae mean my tank is cycled?

It can be said that the appearance of white algae can mean that your fish tank is cycled as algae grow faster on high nutrient levels. We all know that newly established tanks need time to fully cycle and reach maturity so beneficial bacteria can grow.

However, you should remove white algae to avoid its spread and make your tank more beautiful and clean.


This blog gives you all the needed information about water mold and white algae. From now on, you will never wonder about what is the white fuzzy stuff in my fish tank anymore. Providing your fish with a healthy environment is a real challenge.

Dealing with white fuzz isn’t a daunting task, but it takes time. Make sure to clean your aquarium regularly to avoid mold and other harmful things to your pets.

We hope you find this article helpful, don’t hesitate to ask us any questions!