How To Fix A Cloudy Fish Tank (The Right Way!)

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Have you ever thought to yourself “Why do I have a cloudy fish tank and how do I fix it?” 

If so, it’s time to take care of the cloudy mess 

Keep reading to learn how to fix a cloudy fish tank.

Why Is My Fish Tank Cloudy?

A cloudy fish tank can be a devastating sight for us fishkeepers. Many aquarists, including myself, go to great lengths to prevent it.

So when our mostly crystal clear waters start to look murky, it drives many into a panic.

First things first, it’s important to know there’s no single cause of cloudy water. Most issues are small, however some can be devastating to the entire tank.

Determining the issue starts with identifying what color the water is. You can encounter three types of cloudy water which are white, green, and yellow/brown.

Take a second and look at your aquarium’s water. Once you determine the color of your tank’s water, continue reading our guide.

White Cloudy Water

For many new tanks, white cloudy water is a common issue.

The severity of the problem can vary quite a lot. Sometimes, it can take the form of a slight haze or in other cases dense milky like water.

In fact, many don’t even realise the cloudiness. Instead they see it as some dirty glass that needs some quality cleaning.

In more serious cases, the problem is more obvious, with milk like water in the tank.

So, what causes white cloudy water?

Likely Causes

A Dirty Substrate

The simplest reason for the cloudy water is your substrate. Gravel has a fine layer of dust that needs to be removed before it’s added to the tank. If you don’t clean your gravel, all the dust is likely going to be circulated into the water.

Lucky for you, the filter will take care of this. Over the course of several days, your filter will remove the fine particles

In the meantime, the water spout will disrupt the gravel which will cause more dust to kick up. It’s important to be patient during this process and let your filter do the work for you.

Poor Water Conditions

If your substrate is clean and you still notice cloudy water, your water may be the issue. 

For example, in the United States, hard water is used. This water usually contains dissolved constituents, which contain heavy metals, silicates, and phosphates.

Have you ever taken a moment to look at a glass of water from the tap? Many homeowners note cloudy water that turns clear over time. When you fill up a massive aquarium, the cloudiness only intensifies.

Bacterial Bloom

Before you start worrying, this bloom is actually beneficial. When you set up your tank, it must go through the nitrogen cycle.

This process establishes the all-important bacterias needed to help clear waste from the tank. These bacteria will turn your fish’s waste into a chemical called nitrate, which is less harmful to your fish.

Bacterial blooms can occur weeks or even months after setting up the tank. You can even experience blooms after a major water change.

Treating White Cloudy Water

Treating this problem depends on how it’s caused. If residue from your substrate is to blame, you can vacuum the gravel using a water siphon or treat the water with a store bought water clarifier. If you have a strong enough filter, you can also let it do the work of removing the residue.

If your water quality is to blame, you can solve the problem by using Reverse Osmosis (RO) water instead of tap water. Most fish stores will carry RO water, but if you have a larger tank you might want to buy a RO unit, which will be more cost effective in the long run.

Finally, the issue of bacterial blooms. There’s nothing you have to do to get rid of the issue. Your cloudy fish tank should clear up in a week. To speed up this process, you can do partial water changes.

Green Cloudy Water

Green cloudy water, if not treated properly, can quickly overtake an aquarium. The good news is that it’s not harmful to fish!

The bad news? It takes some time to get under control.

Likely Causes

The culprit? Excessive Algae Growth!

In general, aquariums are the perfect environment for algae to grow. In good enough conditions, algae can quickly overwhelm the closed habitat.

There are many types of algae in your tank, but the type responsible for the cloudy green look is called Phytoplankton. This type of algae is so tiny that you can’t see it with the naked eye, resulting in a fogging effect.

So why is algae going crazy in your tank? The answer lies in the location of the tank and the water quality.

If your aquarium is located in direct sunlight, you’re practically feeding the Phytoplankton. Exposing your tank to more than 10 hours of light a day can cause algae to grow at a rapid rate.

The water in the tank can be supporting the algae growth as well. Excessive nutrients such as phosphates and nitrates help algae thrive.

Limiting the amount of nutrients in the water is certainly possible. But it’s going to take some time to get under control.

Treating Green Cloudy Water

So how do you get rid of this green cloud of water?

The first step is to limit the amount of light exposed to the tank. The reason for this is because algae feed on light. Since you’re removing their main food source, they’ll starve off, resulting in a more clear tank.

To start, put a timer on your tank lights. They should be on for no more than 10 hours a day. 

If your aquarium is positioned near a window, consider moving it or block the sunlight with a window covering.

After you successfully limit the amount of light entering the tank, the next step is to lower the phosphate and nitrate levels. The way you do this is by changing the way you take care of your tank. For instant results, do a partial water change. This will remove some of the cloudiness from the tank.

However, the phytoplankton will return if you don’t take other steps.

Take a second and look at your filtration media. Chances are it’s caked in grime. When your filter is not able to catch pollutants in the tank, nitrate and phosphate levels rise. To fix this, simply replace your filtration media.

To prevent the algae from booming again, you need to be more proactive in maintaining your tank. Limit feedings to only a few minutes and remove excess food from the substrate. Also, get rid of any dying plants and other biological matter that can sour your tank.

Yellow/Brown Cloudy Water

The last water color you’ll encounter is Yellow/Brown water. Like cloudy white water, the severity of the problem is based on its cause.

In most cases your water will have a slightly yellow tint from stained decor, but in more severe cases can be seriously discolored, which is a cause for concern.

Likely Causes

In the worst-case scenario, your water is turned to a brown/yellow mixture because of overstocking.

Keeping too many fish in your aquarium is a bad idea on a number of levels. As you add more fish to your tank, less space is available for them to make their homes resulting in fighting over territory. Also, stocking more fish can overload your filter media which can cause spikes in deadly chemicals like ammonia and nitrite. 

Knowing how many fish to keep in your tank is important for keeping crystal clear waters.

If you have an ideal number of fish in your tank and still have brownish water, the issue is likely caused by staining rather than contaminants. Driftwood and decaying leaves produce a substance called tannin.

Tannin is completely safe for your fish. In fact, many freshwater fish thrive off tannin. Depending on the type of fish you’re keeping, tea-stained cloudiness can even benefit your fish. 

Treating Yellow/Brown Cloudy Water

To get rid of Yellow/Brown cloudy water, you need to rethink your tank setup. First, figure out how many fish your tank can hold.

Generally, bigger fish need bigger tanks. Also keep in mind that when you’re buying fish from the pet store, they’re usually infants, juveniles at best. This means that they’ll grow into their adult size over time taking up more tank space as they do so.

Consider purchasing a larger tank or multiple tanks to help prevent overcrowding.

For dealing with stainings through tannins, you’ll need to remove the source. If you have driftwood, pre-soak them to get rid of the tannins. This won’t remove the staining from the water, but instead it’ll prevent the situation from getting worse.

Next, invest in a carbon filter media for your tank. This will soak up the existing tannins from the water, clearing up the water once and for all! 


As you can see, there is a load of potential causes for a cloudy fish tank. 

And while your tank might seem ugly now, you won’t have to put up with it forever!

Knowing what type of color your water is can help you tackle the problem and put an end to the cloudy mess. Following our recommendations for treating your color of water will allow your aquarium to have crystal clear waters in no time.

Now that you have crystal clear waters, want a cleaner aquarium? Check out our guide on how to clean a fish tank!

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Hey there, my name is Gunnar Kennedy. I'm a fishkeeping enthusiast who's been in the hobby for over a decade now! I love sharing new ideas and helping others care for their aquatic friends!

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