Why is Fish Tank Water cloudy? & How to solve this Problem

Cloudy water can be perplexing for most aquarium owners. After all, it can be stressful to see it since you have been doing your best to make the water clear. You might even wonder how it happened in the first place.

There is no definite answer as to why your aquarium is cloudy. In fact, there are many causes why it happens. The solution to the problem varies according to the color and in what circumstances the cloudiness appears.

Fortunately, it is not something to worry about. There are many ways to diagnose cloudy water, depending on the color. We will discuss everything below.

Short Answer

There are many ways to eliminate cloudy water in your fish tank. First, you need to check the color of the water. By checking the color, it will be easy to diagnose the problem.

Regardless of whether the water is white, green, yellow, or brown, you need to conduct regular maintenance to clear the water in your tank. Routine maintenance involves cleaning the tank, changing the water, removing food particles and waste, and cleaning the filter.

While color changes are generally safe, some colors such as yellow to brown can impact the fish’s health. Thus, it’s essential to know the root cause of the problem. In this way, you’ll ensure water uncontaminated by toxic chemicals to keep your fish healthy.

Long Answer & How to solve it

Cloudy water in the fish tank means many things – excess nutrients, bacterial overgrowth, and even too much light. Depending on the type of problem, the water can become white, green, yellow, or brown.

Fortunately, there are things you can do to bring back crystal clear water to your fish tank. These are the different ways to fix cloudy water.

White cloudy Water

White cloudy water usually happens because of an unwashed substrate, bacteria bloom, and dissolved constituents. This scenario usually occurs if you recently changed the water or did not wash the substrates before adding them into the aquarium.

Furthermore, cloudy white water is just temporary. It is easy to eliminate it depending on the root cause. Below, we will discuss how you can solve this problem.


New, unwashed Substrate

It’s natural to forget to wash the substrate before adding it to the aquarium. However, if you notice the water turns cloudy after a few hours after adding the substrate, it is probably the root cause.

Substrates such as gravel, sand, or vermiculite contain small and fine specks. These dust specks are so tiny that it is difficult to notice them in the naked eye.

When adding these substrates to the water, their fine particles will float around your fish tank, causing it to appear cloudy.

How to fix it:

Luckily, fixing cloudy white water due to substrates is easy to fix. Changing the water will help remove the dust that floats around the tank.

Another solution is to wait until the water clears up, especially if you have only placed the substrates recently. If you own filter floss, it will trap most of the dust floating around the tank. Just give your filter more time to get rid of the fine specks.

After the filtering process, the dust will settle on the floor. You can remove the dust using a gravel vacuum that you can buy at pet stores.


Dissolved Constituents

If washing the substrates does not solve the cloudy water in your fish tank, then the reason might be due to high amounts of dissolved constituents.

These dissolved constituents lingering in your aquarium are phosphates, silicates, and heavy metals. They can result in a high pH or alkaline water, which causes the water to appear cloudy.

How to fix it:

You can test the water by using a pH tester. If the water pH is high, use Reverse Osmosis (RO) water. You can buy it from a local pet shop in your area.

Another trick to remove dissolved constituents is to treat the water with conditioners. In this way, the heavy metals will be removed.


Bacterial Bloom

If the water in your fish tank appears to be a thick white fog, then it might be due to bacterial bloom. However, this problem does not occur instantly after setting up the aquarium. The dense cloudy water appears after several days, weeks, or even months.

Bacterial bloom means that the bacteria have grown in numbers which causes the water to get foggy. It might also be due to decaying plants or excess food present in the water.

How to fix it:

To get rid of the cloudy water due to bacterial bloom is to do nothing. The bacteria will disappear eventually after a week.

On the other hand, if the cloudiness appears due to decaying plants, excess fish food, and water, test the ammonia and nitrite levels using an aquarium test kit.

If the results of ammonia and nitrite levels increased, then you need to change the water immediately. Also, cut back feedings for your fish so no excess food will remain.

However, if the food particles in the water are hard to remove, use a flocculant to clear them out. Flocculates allow the food debris to clump together. Then, the filter will be able to remove these particles easily.

Green cloudy Water

Out of all the colored cloudy waters that can happen in your fish tank, green water can panic most aquarium owners. It can be disgusting to look at. It’s also tricky to spot your fish.

So, what does cloudy green water mean? It means there is algae growth, particularly phytoplankton.

Phytoplankton is so small that you cannot see it with your naked eye. However, if it explodes into a large number, it turns your water into a green color.

This type of algae multiplies in billions in a short time. Phytoplankton is not harmful. However, they can be unsightly to look at. They can also block light which the plants need.

Interestingly, some species of phytoplankton are beneficial for your aquarium. They can feed the corals and feed them to tiny fishes from saltwater and freshwater breeders.

However, with most beginner aquarists, the growing numbers of phytoplankton should be eliminated quickly. Hence, we will discuss reasons why green water happens and what you can do about it.


Too much Light

Algaes are plants. It means they love light. However, too much light can send algae into overproduction. Excessive light can come from placing the fish tank in a sunny window, mostly when you leave it for too long.

To remedy green water due to excessive light, avoid placing the fish tank near a sunny area. If it’s challenging to accomplish this, you can put it by the shades drawn by the sunlight or install a background to block the light. If your tank receives bright indoor light, turn off the tank light during the day.

How to fix it:

Another method is to wrap the tank with black plastic or a blanket. Use it to cover your aquarium for a few days. Uncover the fish tank only when you feed your fish. Then, cover it up again.

Using this method will kill the algae within a few days. However, you need to address the root cause of the overproduction of algae.

You can also choose a light suitable for your aquarium. Install an aquarium light timer to control the hours the light should turn on daily. Aquariums with plants need 8 to 12 hours of light exposure.

If your aquarium does not have live plants, you won’t need to light it up frequently. You only need to light your aquarium for about 6 hours or less.


Excess Nutrients

The right amount of nutrients is needed in your fish tank to keep the plants happy and blooming. However, excess nutrients on one type and not enough of another will throw the tank into chaos.

Nutrients come from plants and algae. However, for excess nutrients, the causes might be uneaten fish food, fish waste, dead fish, or water source. When they are in excess or lacking, it could encourage the water to turn into a green color.

Nutrients such as phosphates and nitrates support algae growth when they are not in balanced quantity. Hence, keep these nutrients to a minimum level to eliminate the production of the algae.

How to fix it:

You need to address the problem caused by excess nutrients by checking the water parameters. If there is excess in carbon dioxide, phosphates, and nitrates, lower them by changing the water weekly.

Also, remove the source of excess nutrients such as leftover food or decaying fish. Feed your fish with good quality food to prevent uneaten food. Lastly, avoid overfeeding the fish to prevent the overproduction of fish wastes.

However, changing the water will not solve the problem completely. If these methods did not clear the water, you need to lower the amounts of phosphates and nitrates.


Too many Phosphates

Phosphate comes from fish food and the water source. It naturally increases when wastes are scattered throughout the aquarium.

Phosphate can also enter the aquarium from external sources. These external sources include fish food, chemicals used to buffer the water, and tap water. Other sources of phosphates include:

  • Uneaten fish food
  • Decaying plants
  • Dying algae
  • Fish waste or feces
  • Dead fish
  • Aquarium salts
  • Carbon filter
  • kH and pH buffers

To ensure your fish tank has excessive phosphates:

  1. Test the tap water in your house.
  2. If there is too much phosphate in the water, use Reverse Osmosis (RO) water or a phosphate remover to treat the tap water.
  3. Reduce the amount of fish food for feeding.

Our recommendation for a test kit: Tetra EasyStrips 6-in-1 Aquarium Test Strips

Read more about it here: Best Aquarium Test Kits.

Changing the food to a higher quality can also lessen the number of phosphates since the fish won’t be likely to eliminate often.

You can also do the following steps to lower the phosphate levels in your aquarium:

  1. Change the Water
    Changing the water in your fish tank can lower down the phosphate quickly. However, it is only a temporary fix.
    Continue to change the water to keep the phosphate levels manageable until the root cause is identified and fixed. Make sure to test the tap water since you might live in an area with water with too many phosphates.
    If the tap water contains phosphate, use a distilled or filtered water to buffer the tap one.
  2. Clean the Tank
    Cleaning the tank is another way to lower the phosphate levels in the water. To do this, first, scrape the inside of the tank glass. Remove the gravels, rocks, and other decorations. Clean by scrubbing them well.
    Provide the substrates a good vacuuming. Also, remove the trapped algae inside the filter tank. After cleaning, wait for a few days to stabilize everything in the tank.
  3. Using a Phosphate Absorber
    A phosphate absorber is very useful to lower phosphate levels in your water tank. Add it to your filter tank.
  4. Using a Phosphate Binder
    A binder can be added to the water to precipitate the phosphate out of the water. Use the binder with caution.
    Start with low amounts and gradually work your way up. Note that using too much can turn the aquarium white and affect the condition of the fish. You can buy a binder at your local fish store.

Moreover, after reducing the level of phosphates, you should keep it at that level.

These are some ways you can avoid to prevent the phosphate from skyrocketing into higher levels:

  1. Feed the fish sparingly
    As mentioned several times, one of the known sources of phosphate comes from fish food. You need to feed the fish less frequently and cut back the food portion to feed the fish.
    Pour a pinch of fish food once a day into the fish tank. This amount is sufficient to keep your fish satiated and alive. If there are food wastes left, remove them quickly.
  2. Change the Fish Food
    The reason why phosphate is present in fish food is that it can act as a preservative. All fish food brands are not created equal. Do your research. Choose the brands with lower phosphate levels.
  3. Test the Water Source
    Tap water contains one ppm of phosphate and can be higher. If the water source of the fish tank is tap water, seek an alternate source of water. You can use filtered water to buffer the tap water.
  4. Changing the Water
    Again, changing the water will lower the phosphate level and keep it at a minimum level. Change the water from 10 to 15% weekly. Make sure to use water with low phosphate.
  5. Conduct Tank Maintenance
    Ensure the tank is free from debris and algae as they can cause a buildup of phosphate. Vacuum the tank’s bottom frequently to eliminate uneaten fish food, waste, and decaying plants.
  6. Use a Carbon Filter Media
    Carbon is an excellent filter to use for the tank, but it can increase the number of phosphates. Hence, choose a filter carefully.
    For saltwater aquariums, carbon media serves as a phosphate remover. Other owners combine carbon media and phosphate absorbers to ensure your tank has lower levels of phosphate.
  7. Cleaning the Filter
    Removing the debris from the filter will reduce the sources of phosphates such as food waste and feces.
  8. Treat the Water
    Hard water contains large amounts of phosphate. To address this, use a buffer to condition the water or stabilize the pH levels. Don’t use buffers unless they are needed. If you desire to use them, research the best product with the least amount of phosphate.


Too many Nitrates

Nitrate levels in the fish tank rise over time due to the by-product of fish feces or wastes. To remove them, perform a water change.

Make sure that the filter of your aquarium is clean and suited to the size. In this way, it can capture all the wastes to prevent them from floating into the water.

Lastly, ensure not to overstock the aquarium with substrates, plants, fish, and decorations. Overstocking the aquarium can raise nitrate levels because of the wastes.

Of course, there are more ways to lower the level of nitrates. These are the following considerations to make:

  1. Decorate your aquarium with live plants
    It is necessary to add live plants to your fish tank and not overdo it. Plants naturally produce nitrate that serves as a nutrient and food for the fish.
    When you add too many live plants, it can cause an algae outbreak that can increase nitrate. The abundance of nitrate can turn the water into a green color.
  2. Upgrade to a larger tank or reduce the amount of fish
    Overpopulating your tank can result in a large volume of fish waste. Fish waste, when left for too long in the fish tank, can increase nitrate levels.
    Make sure to keep the fish population at a minimum to prevent nitrate accumulation. You can also consider buying a larger tank if you do not want to dispose of some fish.
    However, resist stocking the larger aquarium with more fish to increase nitrate nutrients in the fish tank.
  3. Reduce the amount of fish food.
    Too much fish food pollutes the water, which spikes the nitrate levels in the fish tank. Hence, avoid overfeeding the fish.
  4. Use a nitrate remover.
    Using a nitrate remover will get rid of the excess levels of nitrates. It also prevents other underlying problems by dissolving organics that contribute to the rising of nitrates.
    Reducing nitrate levels can clear out the water, resulting in a crystal clear one. Make sure to buy a high-quality nitrate remover.

Another way to handle ammonia, nitrite and nitrate is cycling the aquarium. Read more about it here: How to cycle a Fish Tank.

Yellow/Brown cloudy Water

Another color that can appear in a water tank is yellow or brown cloudy water. When you spot this kind of color, it mostly means trouble. Although, there are instances that the root cause of the problem is not too severe.

To make sure your aquarium is a safe habitat for your fish, look into these possible root causes and fix them as needed.


Bacteria Overgrowth

Bacterial blossom does not just make your water turn into a white color. It can tint the water yellow, brown, or green depending on the type of bacteria present in the water.

Some bacteria can elevate ammonia and nitrite levels. These chemicals are lethal to the fish. Hence, perform careful steps to lower them.

How to fix it:

The quickest way to remove the yellow or brown tinge is to change the water in your tank by at least 50%.

This water change level will reduce the number of nitrates and ammonia in your aquarium by roughly half. Test the level of ammonia and nitrites after the water change


Dissolved organic Compounds

Another reason why water changes into a yellow or brown color is because of the dissolved organic compounds.

These organic matter compounds come from fish waste, decayed fish food and plants, and dead fish. These wastes break down into the water, which contributes to a yellow or brown color.

Furthermore, these compounds can impact the fish’s health. Over time, they will be lethal to the fish when not addressed quickly. Dissolved organic compounds can produce unpleasant odors, which makes your aquarium less appealing and attractive.

If uneaten food, decayed plants, or dead fish are present in your tank, perform a cleanup. You can also inspect if the water gets foamy when shaking the tank. It means it has lots of dissolved organics in the water.

How to fix it:

Clean the dissolved organic materials by removing the uneaten food, dead plants, or fish corpse. Perform a gravel vacuum.

Also, inspect the condition of the filter if it is operating normally. Once the filter is running slow, debris can clog. This debris can act as another dissolved organic source.



If you have added driftwood to your fish tank, the tannins will naturally produce overtime which stains the water into yellow to brown.

Tannins lower the pH levels of the water and soften it. Thus, it is not usually a problem. It is recommended to add driftwood for some fishes. However, if it is bothering you, note that the tinted water will clear in time. Tannins from driftwood will deplete eventually.

How to fix it:

You can change the décor in your fish tank to remove the color. As much as possible, remove the driftwood if the color is bothering you.

Keep in mind that if food wastes and other decaying factors cause the tank to get dirty, you shouldn’t clean everything simultaneously. Give the fish a time to adjust with the changes. It will also give the biological colonies to recover.

If you change the filter and vacuum the gravel simultaneously, you could make things worse. Do one activity at a time. Wait for a week before you do another action.

The process of taking one at a time can slow everything. However, the yellow or brown water will remove eventually. Continue doing regular maintenance to prevent problems to reoccur.

Conclusion – Why is Fish Tank Water cloudy?

Excess nutrients, bacterial overgrowth, too much light, food waste, and decaying fish and plants are factors that cloud the water. Fortunately, it is easy to eliminate cloudy water. Some colors are safe, but others can be lethal to the fish.

Water appearing white and cloudy is not much of a problem. It is caused by unwashed substrates, dissolved constituents, and bacterial bloom.

You can address these by performing a water change. You can also use Reverse Osmosis water to lower the tank’s pH since acidity levels can affect the fish’s health. Lastly, remove excess fish food and food waste to clear out the water.

Green waters are safe as well. However, if you are a beginner, it can stress you out.

To eliminate the green color in the water, avoid exposing your aquarium to too much light.

Also, lessen the number of excess nutrients such as phosphates and nitrates. These nutrients can come from fish food, food feces, decaying plants and fish, and water sources.

On the other hand, yellow and brown cloudy water indicates minor to severe problems. If the cause is due to bacterial bloom and organic compounds, changing the water will solve it.

Remove the wastes such as food, fish, and decaying plants that can contribute to the color. Make sure to change the water quickly if bacterial overgrowth and organic compounds are the main reasons your water is turning into a yellow or brown tint. This color affects the health of the fish. Depending on the underlying problem, it can be lethal to the fish.

If you have recently added driftwood, allow the tank to adjust to the color in the meantime. This will also allow the fish to adapt to the new environment and pH levels.

Eventually, the color will become clear again. However, if you’re bothered by the color, avoid adding driftwood into your aquarium.

In general, perform regular maintenance in your fish tank to make sure it does not get clouded. Perform the necessary methods carefully to keep your tank looking good and your fish healthy.


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