Why Is My Fish Tank Cloudy & How To Fix It

A quick and easy guide on how to resolve cloudiness in your fish tank. The fact of the matter is that if your fish tank water is cloudy, it can be caused by a number of factors.

Generally speaking, cloudy fish tanks are caused by the nitrogen cycle not being complete yet, or in other words, new aquariums often see a bacterial bloom.

There are also other causes, such as gravel or sand residue clouding the water, a lack of water changes, an inefficient filter, and more.

Why Is My Fish Tank Water Cloudy?

cloudy aquarium

There are a variety of reasons why your aquarium fish tank is cloudy. Let’s take a look at the main causes of this issue right now.

Gravel or Sand Residue

One of the main causes of cloudy water in your fish tank, particularly in a new aquarium, is gravel and sand.

If you set up an aquarium, and you add the substrate, particularly gravel, the fine powder residue on the gravel can mix in with the aquarium water, thus causing it to become cloudy. Sand may also stir up in the water, whether due to you pouring new water into the aquarium or due to harsh water current.

This is a problem that will usually resolve itself over the course of a few days or weeks., particularly when it comes to the gravel.

Bacterial Blossom

One of the main causes of cloudy water in a new aquarium is a bacterial bloom. If this is the cause, the aquarium water may not get cloudy for a few days, weeks, or even months.

An aquarium requires time to break in, so to speak, and during this time, it is quite normal for the new tank to become cloudy. The reason for this is because your new fish tank has not yet been able to set up a colony of beneficial bacteria.

This, combined with some other factors, such as excessive nutrients present in the new tank, can then cause other bacteria to bloom. Excessive bacteria blooms in the water then cause cloudiness, or in other words, the bacteria become almost visible.

Remember, these are not the beneficial bacteria that your aquarium needs, but other bacteria that should not be present.

Dissolved Constituents

Yet another cause of your fish tank developing cloudiness is due to dissolved constituents. This is a fancy way of saying that the water you have used to fill the aquarium up with contains high levels of silicates, phosphates, and/or heavy metals.

This then often results in the water being very alkaline, and it is often a cause of using tap water. If you are using water right from the tap, it may contain many of these dissolved substances and often requires treatment prior to using it in the tank.

Direct Sunlight & Algae

Another possible cause of fish tank cloudiness is direct sunlight. Of course, sunlight itself does not make water cloudy.

However, sunlight can and does fuel algae blooms. So, if your water is cloudy and green, as opposed to a milky white or grey, you know that algae is to blame.

Excessive Nutrients

If there are excess nutrients in the water, it may also cause algae blooms to occur. Algae feed on phosphates and nitrates, which can be released into the water by decaying plant matter, uneaten food, and fish waste.

How To Get Rid of Cloudy Aquarium Water

Depending on the cause of the cloudy water, there are several steps you can take to get rid of it.

Upgrade or Clean Your Filter

In order to get rid of decaying plant matter, fish waste, uneaten food, unwanted compounds, and bad bacteria, making sure that your filter is working properly is essential.

You need a filter that is big and strong enough to handle the amount of water in the aquarium, the filter needs to be clean and well maintained, and it needs to engage in all 3 major forms of filtration.

Biological Filtration

Related to the above point, ensuring that your aquarium has gone through a nitrogen cycle and features good biological filtration is key.

All of those beneficial bacteria will remove unwanted compounds from the water that can make it cloud up, and it will remove excess nutrients that can cause algae blooms.

Ensuring that your tank has lots of beneficial bacteria is essential. You can also try adding live plants to the tank, as they will support beneficial bacteria.

Water Changes & Cleaning

A good short term solution to cloudy tank water is to perform a 30% water change. Removing old water and adding new water will help reduce cloudiness.

Although, the underlying cause still needs to be taken care of. Also, using a good old gravel vacuum to remove debris that can release nutrients into the water is important as well. Removing any and all debris is essential.

Proper Feeding

Uneaten fish food will release nutrients into the water that algae feeds on. Therefore, removing uneaten food from the mix will help reduce cloudiness.

How long does it take a cloudy fish tank to clear?

This really depends on what the underlying cause is. If you make sure to follow all of the treatment steps listed above, it can take anywhere from 1 to 8 weeks for the cloudiness to totally disappear.

How To Prevent A Cloudy Fish Tank

Here are some tips on how to prevent aquarium water from clouding.

  • Make sure to wash gravel and other substrates before adding them to the aquarium.
  • Make sure to treat tap water for alkalinity and other dissolved compounds before use.
  • Do a weekly water change of 30%.
  • Make sure that you have a good filter, and that it engages in strong biological filtration.
  • Do not keep your aquarium in direct sunlight.
  • When you perform a water change, make sure to clean the tank at the same time.
  • Do not overfeed your fish.

Commonly Asked Questions

Is Cloudy Water Bad For Fish?

If your cloudy aquarium water is caused by a bacteria bloom, which usually happens 2 to 4 days after adding new fish to the tank, then no, it should not be harmful to fish and will clear up on its own.

However, aquarium water can get cloudy if you have soil or water in the tank that is being stirred up. No, this is not great for fish, as it’s not healthy for any organism to be eating and inhaling sand and soil.

Moreover, decaying fish waste, food, and plant matter may cause cloudy water, and due to the fact that these then release ammonia and nitrates, is also harmful to fish.

Will My Fish Die In Cloudy Water?

If this is caused by a small bacteria bloom, then no, it should not kill your fish. However, if the water is cloudy due to decaying natural matter, such as plants and food, as well as fish waste, then yes, your fish can eventually die in cloudy water.

All of those things give off ammonia, and if left unchecked can quickly kill your fish in as little as a couple of weeks.

Will A Filter Clear Cloudy Water?

Generally speaking yes, a good filter should help clear up cloudy water. A good aquarium filtration unit will remove decaying fish waste, plant matter, and old food from the tank, therefore removing sources of ammonia.

Moreover, a good filtration unit will also help to add more beneficial bacteria to the water, bacteria which break ammonia down. A good filter should in all reality help to reduce cloudy water, maybe not eliminate it totally, but it’s definitely a great start.

A good way to control cloudy water is to do regular tank cleaning, to reduce the amount of food you give your fish, to perform regular water changes, and to ensure that you have a high quality filter.

Can I Put New Fish In Cloudy Water?

You really shouldn’t do this. If your water is cloudy, more often than not, it is a sign of somewhat poor water conditions, and these can be caused by a variety of factors. For the most part, you should resolve the issue of cloudy water before you attempt to add any new fish to the mix.


As you can see, preventing or getting rid of cloudy water in your aquarium is not very hard. Just make sure you have a working filter, that there are some good bacteria present, that you change the water often, and that your aquarium is not over stocked. Following the aforementioned tips will in all likelihood prevent cloudiness from ever occurring.

Also remember that the first thing you want to do about cloudy water may go against intuition and common sense, but the first thing you want to do is nothing, at least for a few days, and then if the problem does not go away is when you can start turning to some of the solutions we have talked about.

Image Credit: JohnstonDJ / CC BY-SA

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