White Stuff Floating in Fish Tank: All Reasons & Solutions

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Over the years of fish growing, it is hard to tell how many times I’ve encountered a mysterious white floating material in my tank. I was even worried that my fish’s health would deteriorate as a consequence. That got my researching the ‘white floating stuff’ issue more deeply.

The white floating stuff in fish tanks is typically organic and includes fecal casts, protein accumulation, and Mulm. However, that could also be secondary to an underlying infection, including worms and fungi. In some cases, water that is too hard will appear whitish due to mineral depositions.

As we move forward, I will share a few techniques to prevent your fish tank from getting white. These tricks will keep your water clean, ensuring that your fish do not suffer from fungi and parasites infections.

What is the White Stuff Floating in my Aquarium?

What is the white stuff floating in your fish tank, and what causes it? This question is far more common than you think, and it doesn’t have a single answer because the white stuff that aquarists see in their aquariums isn’t always the same.

In some cases, it looks like dust particles. In other cases, the white stuff is comparable to a series of strings or webs. Some people have observed slime or fluffy debris. Sometimes, this debris moves. Other times, it doesn’t.

The observations you make will ultimately paint a clearer picture of what you might be dealing with. As far as common causes are concerned, the culprit is probably one of the following:

1. Fecal Casts

Sometimes the white stuff floating in your fish tank is fecal matter. Like most animals, fish have cells in the gut that produce mucus that acts as lubrication, allowing the contents of their stomachs to slide through unencumbered.[1]

This mucus allows the fish to poop, and it is always present in your fish’s feces. You don’t notice it because it is usually obscured by the food the fish ate. However, if your fish isn’t eating, it will still pass this mucus. You will see it this time around because it isn’t obscured by food.

If you have ever heard aquarists complain about ‘white stringy poop’, they are probably talking about this thin mucus coating. Some people might confuse the presence of the mucus with a parasitic infestation. But you should only jump to such conclusions if the mucus coating starts to move. Otherwise, it is just poop. To be more specific, it is an empty fecal cast.

2. Hard Water

Before you ask a vet to identify the white stuff floating in your aquarium, double-check your tank to ensure that you can see debris in the water. Your eyes can play tricks on you. Sometimes, people confuse the residue on the cover of their tank with detritus in the water. Remove the top of the tank to verify your assumptions. 

If the water looks clear, look at the tank cover. You will probably observe a white residue resulting from hard water evaporating and causing lime to build up.[2] This is a common occurrence. Whenever hard water evaporates, the heavy elements it leaves behind attach to the glass, creating white residue.

3. Worms

If you can see motion in the tank, the white stuff is probably worms. Aquariums commonly attract detritus and planaria worms.[3] Detritus worms, which look like pointy whitish brownish strings, are not as problematic because they eat animal waste and plant life. They don’t care about your fish.

They enter aquariums via new plants and fish, and they spend most of their time in the substrate, which is why you rarely see them. If your tank is overrun with hundreds, possibly even thousands of detritus worms, you have a problem.

Potential causes of detritus worm infestations include low pH levels and dirty tanks. But again, detritus worms are not that problematic. Yet, the same cannot be said for planaria worms. These flatworms are carnivorous. They won’t attack your fish (unless they are weakened), but the fish eggs are not safe.

4. Body Oil

Your body secretes small amounts of oil that can create a white film in the water. Aquarists have plenty of reasons to place their hands in an aquarium. Sometimes, they have to catch a fish. Other times, they need to scoop leftovers out of the tank.

In doing so, they allow the tank water to wash the natural oils off their skin.[4] Over time, this oil accumulates, forming a film on top. That is even more prevalent if you are using a moisturizing hand cream. The thin layer will quickly wash off your hands once you organize your tank.

5. Protein

Sometimes the white stuff you see in the tank is a build-up of protein. One common source of protein in the aquarium is fish food. Any food your fish doesn’t eat will dissolve, releasing fats and proteins. If you fail to clean your aquarium, and as more food dissolves, the fats and proteins will accumulate, creating an oily film that might appear white. 

Fish poop produces similar results. When your fish consumes its meals, the digestive process produces oils and proteins released into the water along with the creature’s fecal matter. Again, if you fail to clean the tank, and the waste is allowed to accumulate, an oily film will eventually develop in the water.

6. Hardware

Fish food and poop are not the only sources of oil in a tank. You should also consider the filters and pumps, many of which feature moving parts that have been lubricated with small quantities of oil.

When these products are installed, that oil will bleed into your aquarium, creating a white and cloudy film. Also, filters that haven’t been cleaned for a while are likely to accumulate that oil. If you don’t clean them correctly, they will whiten your tank as you put them back in.

7. Mulm

This term refers to the decomposing organic matter in an aquarium. This includes leftovers, rotting plants, and shed skin.[5] Mulm looks like dust, and it doesn’t just float in the water. You will find it in your filters and on your plants, substrate, and decorations.

Mulm is a problem. If left unchecked, it will cause the ammonia concentration in your tank to rise. It will also raise the nitrite and nitrate levels.[6] This is on top of clogging the filter and preventing your plants from receiving sufficient sunlight.

8. Mold

If the white stuff looks like mold, it is probably fungus. This slime is generally found on decorations washed with certain detergents or inadvertently exposed to airborne spores when you took them out of the tank.[7]

You can conclude that you have fungus on your hands if the slime is translucent, and you have to scrub it off your decorations. If it is opaque and you can brush it off with little effort, it is probably decomposition of some sort.

How to Get Rid of the White Fluffy Stuff in Fish Tanks?

Your tank shouldn’t have any white stuff floating in the water, and you should eliminate it the moment you notice it. Some practical solutions include:

1. Feed Your Fish Properly

If the white stuff in your tank is white stringy poop, just make sure you feed your fish. As was noted above, this white mucus appears when your fish isn’t eating. If your fish isn’t eating, you have a far bigger problem than the unsightly nature of white stringy poop.

If you don’t have the time or keep forgetting to feed your fish, I highly recommend considering an automatic feeder. I personally recommend the Zacro Automatic Fish Feeder (link to Amazon). That is one of the few feeders that will pass through large pellets and small ones, without getting stuck.

2. Use Dewormers

Some people use dewormers to eliminate detritus worms. But such medical solutions are rarely as useful as you think, and they are more likely to harm your fish. You are better off cleaning your tank regularly and adequately. Vacuum the gravel and check on the filtration system to ensure that it hasn’t been compromised. 

However, it should be noted that planaria worms won’t respond to these actions. If you know for sure that you have planaria worms, you have to rely on chemical solutions like the API General Cure Medication (link to Marine Depot).

But as you might have guessed, chemical treatments may harm your fish. This is why you should only deploy dewormers after confirming that you have a planaria worm infestation. Talk to a vet before you act. They will show you the dewormers you can use to treat your tank without harming the fish species you have.

3. Change the Water Regularly

Every tank requires a decent filter to remove debris from the water. But even tanks with the best filtration systems require regular water changes to maintain the aquarium’s hygiene. Water changes will combat detritus worms and protein build-up.

Water changes will also keep the algae in the tank at bay. It is the only tool you can rely on to keep your water sufficiently clean. Water changes will also reduce the concentration of toxins like ammonia that are caused by Mulm.

4. Scrub the Slime Off

If the slime on your decorations is a fungus, you can just scrub it off using warm water. Make sure you avoid chemicals and detergents. Just scrub the ornaments with water. If the slime is the result of decomposition, you can still scrub it off if the object in question is solid.

For example, that is the case if the slime is attached to a piece of wood. However, soft objects that absorb the slime are more complicated. If the decomposition is attached to a natural material like a dried-out starfish, you should throw it away before the decomposition spreads.

5. Protein & Oil Removal

If a build-up of protein causes the white stuff, your tank needs more surface agitation. A strong filter should do the trick. Though some people prefer to add air stones. I personally recommend the Hygger Aquarium Air Stone Kit (link to Amazon). That is probably the quickest and cheapest solution.

If you are tired of introducing body oils to your tank, wash your hands thoroughly before reaching into the water. Be sure to rinse all the soap off. Soap is far more dangerous to your tank that body oil. If your hands are not the source of the oil, remove all waste and leftovers. 

You should also look for dead organic matter such as fish and plants. You have to scoop all the rotting organic matter out before it corrupts your tank. Don’t forget to wash your filters and pumps. This will prevent the oil that lubricates their moving parts from bleeding into the aquarium. 

For the most part, regular maintenance is all it takes to keep your aquarium free of all white stuff.[8] If you can maintain proper hygiene in the tank, you have no reason to worry about worms, detritus, oil, or any other form of debris.


Typically, white stuff begins to float in a fish tank when maintenance is on the lower side. That will enhance corruption and residue accumulations. These include protein, fecal lubricants, and Mulm. Those byproducts are considered organic and shouldn’t worry you too much.

However, if the white matter appears on your rocks, decorations, and filters, it could be mold. This case requires your attention since fungi could compromise your fish’s health. Make sure you remove the infected objects, scrubbing off the mold entirely. Soft objects like dried-out starfish or plants should be thrown away.

Generally, regular water changes are the best way of action. That will treat all the potential causes for the phenomenon, including hard water and parasites. Ideally, you should conduct 10% of water exchanges weekly. Do it more frequently if the issue persists.


  1. https://cafishvet.com/2020/01/25/white-stringy-poop-in-fish/
  2. https://www.thesprucepets.com/white-residue-on-aquarium-glass-1381226
  3. https://www.thesprucepets.com/what-are-these-tiny-white-worms-1378753
  4. https://fishlab.com/oil-and-protein-film/
  5. https://nippyfish.net/2007/02/15/yucky-floating-debris-in-betta-tank/
  6. https://aquariumblueprints.com/what-is-mulm-and-how-to-get-rid-of-it/
  7. https://www.thatpetplace.com/articles/Aquarium-Slime
  8. https://animals.mom.me/rid-slime-fish-tank-9704.html