You just set yourself up with a new tank a few days ago and bought a highly-efficient filter to put up with it.

But then you see a speckle of cloud-like formation in an area of the fish tank. Even though you have been continuously keeping the filter on at all times, it does not seem to go away. Rather, it is growing in size as the days pass.

It can be a bit frustrating, I must say. I have faced a similar situation during my early days of fish keeping, not knowing what and why this was happening.

Should you worry about a cloudy fish tank?

Image Credit: Reddit User beckers2012

You might be wondering, how does the water get cloudy? What does the cloudy water denote? What steps can be taken to solve the problem?

These sorts of questions generally pop up in our minds. But finding the root cause can be a bit tricky sometimes.

However, foggy tank water does not always indicate that there is a major issue with the aquarium. But it does give the tank a dirty appearance and it will look bad if you leave it like that.

But do not get anxious- We have scrutinized each reason for cloudy water, and provided fixes for it.

Why is fish tank cloudy?

There can be several reasons for the clouding up of tank water. A few of them are discussed as follows-

Constituents of Water

One particular reason why the water is cloudy or any shade of white or gray can be the type of water used to fill up the tank. This water depends on the source from which it’s been taken.

If we take tap water, for instance, it contains a lot of different metals and heavy metal ions like mercury (Hg), arsenic (As), lead (Pb), etc. Not only that, but tap water also consists of various salts such as phosphates, silicates, nitrates, nitrites, etc.

All of these contribute to the discoloration of water, making it look foggy. Tap water also contains chlorine and chloramine, which can cause problems for the fish if not properly treated first.

New Tank Syndrome (NTS)

If you have bought a new tank, chances are that it will come with fresh substrates such as gravel or sand. If you fill it with water and see the water turning cloudy instantaneously, that means the substrates have not been washed properly yet.

Another reason would be the tank walls themselves. Sometimes it inhabits dirt and other stuff when stored for a long time in warehouses. So, they also need to clean carefully to avoid getting dirt while filling it up with water.

Apart from this, the growth of various bacteria is also a part of New Tank Syndrome, which can lead to the fuzzy appearance of the tank water.

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Bacterial Bloom

Image Credit: Reddit User ibarney64

The cloudy appearance of the water due to bacterial growth does not always show the moment you assemble your tank. Rather, it shows up after many days or even a week. It can take some time for the bacterial colonies to grow in these conditions after a few days of exponential division.

This phenomenon is natural; it usually takes a few weeks to even months for the tank to come up with a solution by itself. Some beneficial microorganisms also take time to establish themselves, but in turn will help with breaking down waste products and remaining food particles.

This is a natural life cycle for a new tank. It will happen with every tank till the beneficial microorganisms have established themselves in the new biochemical environment of the tank. After a while, when everything is balanced, the water will automatically start to clear up.

Inadequate filtering system

Cloudy Aquarium Water Causes

Many fish keepers, while building new tanks, care less about installing a quality filtration system. A filter means it will not be able to properly clean the tank up to the requirements.

This can lead to the accumulation of food substances and feces of the fish, causing a massive hike in the number of microorganisms present in the water.

This can result in a cloudy or hazy appearance of the water. Some microbial colonies can also lead to different colorations.

6 ways to fix cloudy aquarium water

There are multiple ways by which we can fix the haziness of the water. However, it may take some time to find the culprit responsible for it and come up with a proper fix. Here are six things that you can do to fix it-

Softening of tap water

As tap water consists of a lot of heavy metal ions along with various salts, it is considered very harsh. So, to remove the harshness, we must use conditioners and softeners that will help to mitigate it.

The supply tap waters also contains a good concentration of chlorine and chloramine. Potassium metabisulphite pills can be used to remove excess amounts of chlorine and chloramine from the supply water.

Alternative to tap water

In addition to that, you can also opt for aquarium water that is readily available in most aquarium shops. These come already treated with beneficial salts for your fish.

If it is possible, you can also use drinking water from an RO (reverse osmosis) filter if you have one in your home. RO filters are very good at removing heavy metals contaminants and also filtering out the salts which make the water hard.

Settling of bacterial bloom

If the fuzziness is due to a bacterial growth, then you should not worry much. If your tank already contains fish inside, then you could transfer them to another place until it becomes clear, only if you suspect they are uncomfortable.

Generally, a bacterial bloom is a natural thing that happens when you buy a new tank. However, it is cleared up eventually, but it may take a few weeks to even months. It is similar to the life cycle of a new tank, which eventually finds its own balance.

Replenishing of tank water

Replenishing tank water partially on a weekly to a bi-weekly basis can prove to be very beneficial. If you can manage to replenish the water completely, that’s even better. But this is much more time-consuming than changing 20 to 30% of the water on a routine.

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Vacuuming debris and food matter

It is not uncommon for fish keepers to overfeed their fish sometimes. However, this can lead to production of excessive waste and leftover food.

If they are not vacuumed up properly, it can change the chemical properties of the water after a while. This can lead to increased nitrate and phosphate levels, promoting excessive bacterial and algal growth.

But the growth of microorganisms isn’t the only thing that makes it foggy. The particles themselves stay in a colloidal state with the water, giving the tank water a cloudy appearance.

Use of Flocculants

If there is waste that you are not able to remove with a vacuum, then you can use flocculants. These are chemical substances that help particles of a colloidal solution clump up and come out of the solution.

When they are clumped up, they settle down as sediment that can easily be scooped or vacuumed up. An example of flocculant is polyaluminium chloride. These can be purchased online or from local shops.

Green cloudy tank water

Green and cloudy fish tank water

Sometimes, instead of getting a white foggy haze, you can get a green cloudy appearance. It is actually a different phenomenon from the white one. It can occur in different shades of green as well.


The reason for the green cloudy effects is an algal bloom. An algal bloom is similar to a bacterial bloom, where the algae starts growing unhindered. As you know, algae are microscopic plants, so they are green in color due to the presence of chloroplasts.

Some species of algae do not just stick to surfaces and grow; they float in the water, creating a cloudy suspension-like appearance.

These can come into your tank by accident whenever you are buying plants or other items for your aquarium. However, it is a bit tricky to get rid of them because of their invasive behavior.

Ways to fix it

Getting rid of algal blooms can take some time. But there are strategies we can apply to our daily hygiene work to lower their good growth conditions.

Change tank lighting conditions

Plants make food from light, and so do algae. So, the presence of bright light can also induce excessive algal growth. In order to control that, we must reduce the amount of light they are receiving.

Change to a low-brightness lamp and also reduce the hours the tank receives light. After a few weeks, you will start to see the green color fade away.

Algae won’t be able to make adequate amounts of food for themselves and will slowly start to die. This, along with a good filter, can help clean up the remaining debris in the water.

Reducing the number of residual phosphates

These phosphates come from waste organic matter from fish food and waste. If they are not cleaned up from time to time, it can lead to increased phosphate levels.

These act as growth-promoting factors for plants, including algae. So, we need to reduce their concentration by replenishing water on a regular basis. Installing a highly efficient filter will also contribute to reducing the level of the water.

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Additionally, tap water also consists of phosphate salts, which will definitely help the algae grow. In this case, you should change the water immediately if you suspect the water is hard.

Reducing the nitrogen concentration

As we know, nitrogen is a well-known plant fertilizer. It is a very important micronutrient for their growth, just like phosphates.

And just like phosphates, the leftover fish food and feces release good amounts of nitrates and nitrite when they decompose. Thus, the solution is the same as in the case of phosphates; keep the substrate clean, avoid overfeeding the fish, install a good filter, and inculcate the habit of changing and replenishing the water at regular intervals.

Yellow tank water

More often than not, the water can also turn yellow, or sometimes an amber or golden-brown color. However, this is not a frequent case, but it does happen, leaving people confused.

Reason for yellow coloration

The most common reason for the abnormal yellow color of the water is due to the presence of tannins. Often, people bring plants, leaves, and wood pieces from the wild to put in their tanks to decorate them.

But those plants’ parts may contain tannins that are naturally present in them, even if they appear green or brown. These tannins are released into the water after a while.

These tannins can lower the pH of the water to some extent. However, this lowering of pH can be favorable to many fish species and can serve as a good breeding place.

How to fix your yellow tank water

Yellow and cloudy fish tank water

As tannins are dissolved at a molecular level, it is hard to remove them just by using a filter. However, you can remove the leaves or wood pieces that you suspect are releasing the tannins.

But, even after removing them, it can take a few water changes to revert it back to normal.It can take a few weeks for the water to become colorless again.


Why won’t my fish tank’s cloudy water go away?

Cloudy aquarium water can be due to various reasons. However, if the bacterial bloom is the reason, then it will take some time to go away. All you can do is maintain strong hygiene and be patient. It takes some time before the tank’s life cycle stabilizes and comes to a balance. This is where the water will start clearing up.

Will cloudy water hurt my fish?

It may seem dangerous, but it is absolutely normal. All you have to do is be patient and wait out the cloudiness. However, you should always keep an eye on the fish anyway, even if the water is clear.

Why is there white slime present in the fish tank?

The presence of white slime is due to white algae. These algal colonies have a cottony, slimy appearance. These are not harmful to the fish but can grow very fast under the right conditions. Controlling them is the same as controlling any other algae. However, you can put snails and shrimp, which are known to eat algae and other waste products. Additionally, you can also put fish, especially those that eat algae, such as Chinese Algae Eaters, Siamese Algae Eaters, etc., which will clean up the algae at a faster rate.

About the Author

Shelby Crosby

Shelby is a passionate fishkeeper who has been writing about fish for over 5 years. She is a pro aquarist and holds a BSc Honors Degree in Wildlife and Fisheries. She creates her own beautiful aquarium layouts and loves to share her knowledge of tropical fish with other hobbyists.

Career Highlights:

  • Has worked with several aquarium manufacturers as a consultant
  • Organized and hosted workshops on freshwater fish keeping at retail stores, educational facilities, and libraries
  • Released content for the amphibian community through her writings

Educational Highlights:

  • BSc Honors in Wildlife and Fisheries in 2011 (University of Northern British Columbia)
  • Completed her undergraduate thesis on the effects of zoochlorella supplementation on the growth and health of fish.

Writing Experience

Miss Crosby is a Freelance blogger; many of her articles are posted online on various blogs. She has also written a few short articles for "Tropical Fish Hobbyist Magazine" in the past. She is a regular contributor to Her education, first-hand experience with fishkeeping, and in-depth knowledge in aquaculture make her one of the most competent writers in the industry.

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