White Algae In A Fish Tank – Causes, Removal, & Prevention Tips

    White algae in a fish tank

    White algae in a fish tank is something most aquarists have to deal with at some point. The coarse threads are very unattractive. And they are too stubborn for even a high-quality filter to remove. Is white algae a sign that your aquarium is about to fail?

    White algae is not a major cause for concern. It is a sign that you have a large source of decaying organic matter. Driftwood and dead plants are the most common sources. Proper preparation of new pieces of driftwood and removing any dead plant leaves or fish will remove the food residue that white algae need to survive, effectively removing it from the tank.

    That said, if your white algae infestation is thick enough, you may need to do more. The white fuzzy stuff can look like cobwebs covering your tank! So how do we get a tank clean of white algae?

    White Algae In A Fish Tank – What Is It And What Does It Look Like?

    Weather spined loach (Cobitis taenia)

    White algae in fish tank is not as common as green or red algae growth. That is because white algae is not technically a true algae.

    Most kinds of algae are either cyanobacteria (blue-green algae) or plant-like organisms. Some are unicellular (green water) while others are multicellular (green hair algae). And all of them play an important role in providing oxygen for air-breathers like us humans!

    Black beard and staghorn algae are forms of red algae. They are different from green algae but can be treated similarly.

    White algae growth comes from bacteria or filamentous funguslike organisms. Sometimes the patch of white fuzzy slime is a mixture of the two types of organisms.

    Many are more properly thought of as a kind of mold. This form tends to stay short and fuzzy. You may see patches of it on excess food that a fish does not eat. But this form disappears quickly once the food residue runs out.

    Other white algae growth are true fungal infections. They can spread in massive white algae mats, covering live plants, driftwood, rocks, and your substrate. These mats are common in a newly set up freshwater aquarium.

    Where Can I See White Algae Growth?

    White algae is very uncommon in saltwater aquariums, however. Not because the organisms that cause it are predominantly freshwater. It’s more due to the fact that freshwater aquariums tend to have more organic-based decoration choices.

    Saltwater tanks tend to use live rock and corals. These don’t offer much of a food source for white algae growth.

    This video demonstrates nicely what a patch of white algae growth looks like, as well as some additional ways to control it:

    YouTube player

    What Causes White Algae In A Fish Tank?

    What causes white algae in a fish tank
    Siamese algae eater (Crossocheilus oblongus)

    Green algae is the bane of every fish-keeping beginner. It is an organism related to plants. Therefore, too much light and nutrients in the water column are the usual causes.

    But as you can see from the color, white algae is not a photosynthetic organism. Its lack of greenery means it has no chloroplasts to harvest light with. This means that lowering your light levels won’t get rid of white algae.

    As a colony of bacteria and fungi, white algae feeds on leftovers and decaying organic matter. Aquarists often have a white algae outbreak for the first time when they add a new piece of driftwood to the system.

    White Algae And Driftwood

    Driftwood that has not been soaked for a long time will develop soft patches that microorganisms love to consume.

    When you add new driftwood to a tank, the harder wood beneath it will remain for years. But the softer outer layer will start to decay. The beneficial bacteria help keep your tank clean by consuming organic matter before rot-causing germs can.

    As they do so, the bacteria and water molds form thick colonies on the tastiest spots of soft wood. These colonies become visible white algae.

    Sometimes the water mold will remain short and compact. But other colonies will grow long and stringy. It all depends on the species of bacteria, fungi, and water mold that starts feeding.

    Dead Plants In An Aquarium

    Another route for white algae to take hold is to leave too much dead plant matter lying around. Decaying plant leaves are similar to driftwood in their nutritional content.

    They won’t form patches of white algae right away. But if left untrimmed, you will start to see stringy water molds take shape.

    Dead Fish And White Algae

    Have you ever had any of your fish pass away during the night? Only to find them covered in a cottony growth of white mold the following day? This microorganism slime is the same thing as white algae.

    This excess growth of water mold occurred so much faster on your dead fish because they are a much richer source of food than dead plants or driftwood.

    Fish are loaded with protein, fat, and other nutrients that microorganisms love. This is why you want to remove them ASAP. Otherwise, your ammonia levels will start to rise.

    You should also look for signs of stress in your other aquarium fish. Do any aquarium filter maintenance you have been putting off. And perform a water change if the parameters aren’t where they should be.

    A dead fish is a sign that it’s time to check on the rest of your aquarium inhabitants.

    Improper Feeding Techniques

    If you see what looks like white cotton growing on leftover flakes and pellets, it’s a sign that your water is saturated with white mold spores. The faster you see white fuzzy stuff form, the more germs there are in your tank water.

    The problem here is that high nutrient levels + water + warmth is an ideal breeding ground for germs. Even an aquarium filter is not going to do much for microscopic bacterial and fungal spores.

    White algae is especially common in unfiltered betta and goldfish bowls. Not because the filter would remove spores. But rather, there is not enough surface area for a proper biological cycling process to form.

    And when you overfeed your fish, this leftover food simply rots. Providing a ready source of food for white fuzzy stuff to grow. Fish waste will also grow white fuzz in dirty aquarium water.

    How Much Do I Feed My Fish?

    The first thing you should do is to adjust how you feed your fish species. Do your best to only feed as much as your fish will completely consume in a single meal. Even if that means underfeeding slightly.

    Fish really don’t need all that much to eat. As a rough rule of thumb, a fish’s stomach is about the size of its eye. This is less true with the larger your fish are. But for smaller fish like guppies, bettas, and tetras, the rule works well.

    Make Sure You Have Adequate Filtration

    Second, check to see if your filtration is up to the task. If your tank is overcrowded or you are feeding too often, it may not be able to keep up with the bio-load. Especially in tanks where the beneficial bacteria are not fully established.

    And if you have no filter at all…You should really think about adding one! Filters are inexpensive to buy and maintain.

    A small sponge filter will do a lot to help reduce the build-up of organic waste in a small aquarium. This model by UPPETOOLS provides plenty of ammonia and organic-reducing capacity!

    Is White Algae Bad For Fish?

    Is white algae bad for fish
    Gold freshwater angelfish (Pterophyllum Scalare)

    The answer here is that it’s complicated. Every aquarium has some of the bacterial and fungal species that cause the white fuzzy growths.

    And that’s not a bad thing! You want a diverse microorganism community in your fish tank. But the rapid growth of white stuff is a sign that your water is full of mold spores.

    These spores are opportunistic. It’s only when there is a large amount of excess nutrients that these germs get out of control.

    White “algae” is not immediately harmful to healthy fish. They can have a direct negative impact on sick and injured fish, though. Open wounds and torn fins in our aquarium pets offer an immediate entry point for spores.

    A healthy fish may be able to fight off a fungal infection. But the conditions that support white algae growth tend to be high in ammonia and other pollutants.

    An aquarium with poor water conditions will suppress the immune system of your fish. Which allows opportunistic germs like white fuzz to take hold. This form is better known as fin, mouth, and body fungus.

    How To Treat Body Fungus In Aquarium Fish

    Fungal infections in aquarium fish look similar to the growth of white fuzz on decorations. The fungus and bacteria will form slimy patches. These can be translucent to pale white in color. Inflamed skin and blood vessels may be visible as well.

    When you see white fuzz on your fish its a sign that you need to take serious corrective steps. Medications like methylene blue and PimaFix are my recommendations.

    If possible, move any sick fish to a quarantine tank. Here, the fish does not have to fight strong water circulation since you usually use a sponge filter on a hospital tank. It can also eat and swim freely without competing with the other fish.

    The main tank likely needs a partial water change. I would start with 30-50%. Also dig deep into the gravel with your siphon hose. You want to remove any excess organic debris that’s fueling white algae growth.

    After you do a water change, test the water parameters, just to be sure. If you see signs of any ammonia, nitrite, or nitrate, do another one to bring concentrations down to safe levels.

    How To Get Rid Of White Algae In A Fish Tank

    How to remove white algae
    Wagtail Platy Fish (Xiphophorus maculatus)

    White algae is rarely dangerous unless it infects aquarium fish directly. It is more of an indicator that there are excess nutrients not being used by more beneficial microorganisms.

    This imbalance commonly happens when you accidentally overfeed your fish. Or when you go too long between water changes or maintaining your filter.

    An undiscovered dead fish can also trigger a white algae bloom. Once you get the nutrient levels inside your tank under control, white algae does not take long to disappear.

    You can get the nutrient levels inside your tank under control by performing a 50% water change. Be sure to dig deep into the substrate to remove any excess food.

    And if your filter has not been maintained in some time, replace any expired media with fresh material. Once you do so, white algae does not take long to disappear.

    You can also help the process by using a stick or the handle of your net to remove long threads in your tank. Especially if it’s growing over living plant leaves. Any dead leaves with white algae patches need to be trimmed away.

    White algae on aquarium glass or decorations can be gently removed using a hand algae scraper. White algae is actually easier to remove than most green algae varieties.

    How Long Does It Take To Remove White Algae?

    White algae growth will disappear within two weeks, at most. The microorganisms have to run out of food first. Once they do, they die back very fast. If white algae growth persists, it means that you still have nutrient levels that are too high.

    How To Prevent White Algae From Growing In Your Aquarium

    Maybe you’ve already dealt with a major white algae infestation before. So how can we prevent white algae in fish tanks from ever coming back?

    Increase Aquarium Water Circulation

    Water movement plays a major role in the formation of long threads of white fuzz. The short, fuzzy growth pattern can form in any aquarium. Even ones with strong circulation.

    But the threads are quite fragile. In tanks with little to no water circulation, you may see the long cobweb-like growth of white fuzz algae.

    A simple water pump is all that is required here. The pump will also help oxygen and heat circulate better around your aquarium. Bear in mind that the main cause of white algae (high levels of organic matter) still need to be addressed, though!

    Add a UV Sterilizer

    UV sterilizers are more common in the saltwater hobby when pristine conditions are needed for stony corals. As well as outdoor ponds for controlling green water algae.

    An aquarium UV sterilizer is a great control method for white algae growth as well. Any floating spores will be eradicated. But not any white algae that is already present and established.

    Keep in mind that excess nutrients are still the real problem here. These will continue to cause a rise in ammonia from other aquarium bacteria. You still need to deal with that through better filtration, a feeding adjustment, water changes, and so on.

    Chemical Control Methods

    You can also try chemical control methods to kill off your white fuzz. The exact medication depends entirely on whether you have bacterial or fungal-based white algae growth.

    Unfortunately, this is almost impossible to determine unless you have a microscope. Bacterial growths tend to be stringier. While fungi form thick, cotton-like mats that don’t grow so high. You can also get a mix of the two at times.

    Malachite green is an anti-fungal remedy. Its most often used in the aquarium trade for body fungus and fungus on fish eggs. When treating an entire tank, be sure to research whether your organisms are sensitive to it.

    Generally speaking, copper-based medicines cause the most issues. But sometimes a fish can be sensitive even to “safe” medicines. Especially scaleless fish like kuhli loaches or spiny eels.

    What Eats White Algae In A Fish Tank?

    White algae eaters
    Amano shrimp (Caridina multidentata)

    When trying to keep a fish tank clean the topic of algae eaters always comes up. After all, algae is a fact of life for fish keepers. So are there any algae eaters that are willing to eat white algae?

    Unfortunately, very few species will see this white fuzz as a food source. That includes nearly all fish, including plecostomus, otocinclus, and mollies.

    Invertebrate algae eaters are a different story, however:

    Amano Shrimp

    Amano shrimp will eat white algae. In fact, these animals feed on microbial biofilms of all kinds. Amano shrimp also grow large enough to live with most smaller community aquarium fish. Larger fish will be tempted to eat them, however.

    Scientific Name: Caridina multidentata
    Size: 2 inches
    Lifespan: 1 to 2 years
    Temperature: 65-75°F

    Nerite Snails

    Nerite snails are also one of the best algae eaters, in general. They eat white, green, and even black and staghorn algae. They also can’t reproduce in freshwater so they won’t take over a tank the way ramshorn snails do. I add nerite snails to all of my aquariums!

    Scientific Name: Neritina sp.
    Size: 1.5 inches
    Lifespan: 1 to 2 Years
    Temperature: 70-80°F

    Does White Algae In An Aquarium Ever Go Away On Its Own?

    Armored catfish (Corydoras aeneus)

    White algae can go away on its own when the nutrients fueling it in your tank run out. But that may not be so easy to do. Especially if your tank has a high number of aquarium fish. All that fish poop and leftover food will help fertilize white algae growth.

    It is better to be proactive in controlling white algae. It is a sign that your aquarium nutrient levels need correction. And the sooner the better.

    White Algae On Driftwood

    The only time I’d recommend waiting and watching is if you have white algae growing on a piece of driftwood. This is very common when adding a new piece to your tank.

    You can scrape it away if you wish. But as long as your water parameters are normal the white fuzz won’t spread. Once the white algae uses up the nutrients found in the softer portions of driftwood, it will soon die off.

    You can hasten this by pre-boiling any driftwood you buy before adding it to your tank. This helps slough off any soft patches of decayed wood.

    Boiling also draws out more of the tannins that will impact your water quality. Most pet store woods are safe, and many are even pre-boiled.

    Always boil any driftwood you find in nature. It not only likely has rotting patches that are white algae food. It can also house parasites, animal eggs, and other unpleasant surprises for your fish.


    White algae on aquarium plants and decorations is a sign that something needs correcting. It’s better thought of as water mold since it’s a mixture of bacteria and fungi.

    That said, you can control water molds by feeding less and performing more water changes. If the growth is too severe, you might even try chemical methods of control. But rarely is white algae dangerous to your aquarium pets!

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