Cloudy Fish Tank Water: How To Distinguish and Get Rid Of It

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A cloudy fish tank can be a nightmare for many fishkeepers. Not only it’s unpleasing to look at and prevent you from fully enjoying the aquarium’s beauty, but cloudy tank water can also sometimes be dangerous for the living creatures inside it.

To be able to solve and prevent cloudy water from coming back, you need to identify the water characteristics and the circumstances you’re facing.

Today, we will discuss everything you need to know about fuzzy water to get you prepared and equipped. Let’s dive right in!

Why is My Tank Water Cloudy?

Unfortunately, there is no single solid answer to this question. There are several reasons why your tank water turned murky, and that makes your overall tank atmosphere gloomy.

The specific reasons all depend on what color your cloudy water is. Different colors, different causes. The variety of cloudy colors is white or gray, yellow or brown, and green. But usually, most cloudy water is due to the nitrogen cycle.

You can easily notice it through your tank. Maybe one day you walk past the aquarium, and you see a color change, then you have to stop for a while and observe. You can also scoop some of the water out with a plastic cup or any container that is white-colored inside.

Because the causes of each cloudy water vary, there will also be different effects, handling, and prevention. We will discuss each of them shortly.

Is Your Aquarium Water Milky White or Grayish?

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It looks exactly as how it sounds. Milky white or gray water looks like you mix your tank water with some milk. Or with a lot of dust until it becomes murky and blurry. You may still be able to see your critters, but it won’t be fun as when you see them in crystal clear water.

In most cases, white or gray water is not something you need to be extremely concerned about. But in some extreme ones, the water might turn so turbid that you can’t see anything inside it. There are a few causes of gray or milky water, and we have them listed below.

New Substrates

The first suspect is the substrate. White cloudy water especially happens if you have a recently established tank or you have just added new substrates into it. The usual target is a one-day-old (or hours old) fish tank.

Although substrates are already coated with epoxy, there will still be a lot of fine dust. But where does the dust come from? Well, you might carry and handle the new gravel very carefully. But did you know what the gravel have gone through before it got to you? People from the producing companies or fish shops might just toss or throw the bags of gravel to its place.

Therefore, the gravels break and produce dust residue. You may not notice them when you pour the substrate into the bottom of your aquarium. But soon, you will notice dust being circulated in the water and sticking onto the aquarium glass, which makes it hazy.

Solution & Prevention

The first solution is to do nothing. Which doesn’t sound like it could improve the situation at all. But that’s how it works sometimes. White or grayish water can vanish by itself within hours, but it can also take days. Regardless of the time, you can just let aquarium nature do its work.

But there’s actually something better you can do rather than just waiting. You can perform a water change of 50% to let some of the dust flow away. Or even better, empty the tank to rinse the substrate thoroughly.

The best way to clean the substrate if your tank water gets cloudy (or before you put it inside your tank) is to take a small amount at once and put it in a basket. Then, use a garden hose or just straight from the tap to fill the basket and let the water flow out. Remember, do it slowly with a small water stream. Once the water comes out clean, it means you’re good to go.

Another thing you can try is to use a gravel vacuum (if you have one) to clean the substrate. Gravel vacuum has a pretty strong sucking power which can help you to get rid of the fine dust residue from the dirty substrate.

And last but not least, try to use polishing filter pads. The pads will help to trap the dust particle, and hopefully, makes the water clear again and keep it that way. It also won’t cost you a lot.

Water Conditions

Let’s say you already cleaned the substrate thoroughly and carefully. You have also made sure and double-check that the water that flows out of the bucket is already clean. But for some reason, the white cloudy water persists.

Then, the culprit could be the water itself. This is another possibility of what causes milky white or gray cloudy water. The water that is used contains high levels of dissolved constituents. These include heavy metals, nitrates, phosphates, and silicates.

In some areas, the tap water is hard. You can check if hard water is used in your area by getting some tap water in clear glass. If the area where you live uses hard water, you will notice the hazy water becomes clearer after a while.

Perhaps it doesn’t seem like a big deal in a small amount. But if you use this water to fill the tank, the result will be bad.

Solution & Prevention

To fix poor water conditions, you can first test your tank water using a water testing kit. This testing kit will most likely show you that your aquarium water is alkaline, which means it contains a high pH level.

If that’s the case, you can try using a tap water conditioner. The water conditioner will neutralize the dangerous stuff in the water, like chlorine, heavy metals, and ammonia.

There’s also one more thing you can do to improve the water conditions, and hopefully, preserve it as well. So instead of filling the tank with tap water, you can use RO (reverse osmosis) water.

Most fish stores sell prepackaged aquarium water. This is an option if you have smaller tanks. But if you own larger ones or more than one tank setup, purchasing an RO unit to produce RO water is a better idea. It will save you some money in the long run.

Bacterial Bloom

Another common cause of milky white or gray water after a new aquarium is settled. However, the cloudiness in the water doesn’t form right after you finish your tank setup. It might take days, weeks, or even months. It can also happen in mature tanks with critters living in them.

When you see your brand-new tank water gets fuzzy, it could be a bacterial bloom caused by the heterotrophic bacteria. No, these are not the beneficial bacteria that are colonizing in your filter. Those good bacteria that oxidize the ammonia and nitrites are called autotrophic. While this, the heterotrophic, is the one that makes plant detritus, leftover food, and fish waste rot and produces ammonia in your tank.

Generally, heterotrophic bacteria are present in all aquariums. In a small number, they won’t bother the tank inhabitants. But if there’s a population explosion of bacteria, that’s bad news. Millions (or billions) of heterotrophic bacteria is what makes your tank water cloudy.

So, what causes the significant increase of heterotrophic bacteria? There are a few possibilities. It can be uneaten food that’s left in the tank, dead critters, or plant debris. In short, too many nutrients in the water columns cause the bacteria to multiply in a fast amount of time. It can also be due to poor filtration or even over-cleaning it. Cleaning your filter too often will wipe out the good bacteria in it.

Solution & Prevention

There’s not only one solution to tackle down the bacterial bloom. That’s because the things you need to perform in a newly established tank (without aquatic life) and a mature tank (with critters in it) are different.

In fishless tanks, you don’t need to do anything. Just wait and trust the process. You can let your tank go through the break-in cycle, which is completely normal for new aquariums. The bacterial bloom will eventually disappear by itself because the heterotrophic bacteria will die after they are done eating the organic substances.

On the other hand, if you own a mature tank with living creatures in it, you need to do something. To kick the bacterial blossom out of your tank, you can:

  1. Perform a water change regularly. You can change around 20 to 25% of the water every few days. If you need to change the water more than the amount mentioned, add a filter-boosting product in the water.
  2. Try to use flocculates. It is a water additive that makes the small debris particle that floats in the water lump together. The lump will then be removed by your filter efficiently. It is usually called water clarifiers in stores.
  3. Check the ammonia level every day and increase aeration by adding a powerhead or an airstone near the surface.
  4. Reduce the food portion to prevent any uneaten food left in the tank.
  5. Take out decaying plants, leftover fish food, or dead critters immediately to keep the water in a good condition.

Is It Cloudy Green?

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Green murky water in the aquarium looks terrible, and it is perhaps the toughest one to tackle down. But don’t be discouraged. There are still ways to throw them out of your tank. So, what causes it? Excessive algae bloom.

But these algae are not the same as the ones you see sticking on the tank’s glass or decors surfaces. Instead, they float freely in the water. These microscopic algae cells are called Euglena, and they have flagella, a hairlike structure that makes them able to move around. They usually swim to get closer to lights, which is one of a few things that help them grow.

Some say that these planktonic algae are not necessarily dangerous, as they are always present in any aquatic life. However, they can deplete oxygen levels during the night. So that’s a reason to get rid of them.

Before you can decide on what action to take, you need to know what causes algae to overtake your tank. Below are a few things that trigger the algae bloom, as well as the solutions.

Excessive Light

Exposing your fish tank to natural light or letting the aquarium lights on for too long is a reason for an algae bloom. By doing so, you’re feeding them and giving them a boost.

Solution & Prevention

The ideal time for lighting is around 8 to 10 hours a day. So, if you’ve been letting your tank lights on for longer than that, you need to reduce that. Try setting the timer to automatically turn the light off after 8 to 10 hours.

Your tank’s location can also play a role here. If by any chance, you have your aquarium near the window or anywhere directly exposed to sunlight, you might want to move them. But you can also try using window shields or any light-blocking material on your aquarium glass that’s unprotected from sunlight.


An ideal nitrate level in every aquarium is not more than 20ppm (parts per million). Above that, it will make the algae in your tank overgrow. Nitrates are fertilizer to plants and algae, and that’s why they can help algae to thrive.

It comes from uneaten fish food and fish waste. If your aquarium is overcrowded and you feed your tank inhabitants too much, this might be the cause of why your tank water turns green.

Solution & Prevention

One thing you need to do is decrease the nitrate level. You can do it by changing the water by around 30% to 50% to give immediate relief. Following that, do a water change of 30% every week to maintain water condition.

Besides changing the water, you will also need a good filter system. If you notice the algae bloom, try to use a diatomic or micron filter to take the algae cells out from the tank. Using UV Filtration is also beneficial during this situation since it will kill the cells, and therefore, reduce the algae and fuzzy green water.

To prevent leftover food from rotting in the tank, make sure to feed your fish just as much as they need. Usually, all food will be gone within 30 seconds (or two to three minutes for slow eaters).

And last but not least, a friendly reminder to not house too many critters. More fish means more bioloads. So, keep just as many as your tank could.


There are a few things that cause a high level of phosphates in the water. First, decomposing organic compounds in the water like dead fish, rotten plant matters, and fish waste. Second, it can also come from commercial fish food as some companies use phosphates to preserve them. And lastly, it may be the water itself.

Just like nitrates, phosphates are also an excellent fertilizer to encourage algae growth.

Solution & Prevention

Maintaining your tank water to always stay in its best condition is vital. Just do a regular water change every week. In addition, always remove uneaten food or dead plants as soon as you see them. Vacuuming the substrate is also a good option to get rid of leftover food and fish waste. And again, do not overfeed your fish to prevent leftover food.

Lastly, if you think the problem relies upon the water, then try to test the water first. If the result says that your local water contains high phosphates, switch to RO water. It may not be the cheapest solution, but it’s best for your tank inhabitants.

Is It Yellow or Brownish?

Yellow or Brownish Fish Tank Water
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This is a pretty uncommon type of cloudy water to happen. But it does occur in some aquariums sometimes. Yellow or brown water looks filthy and gloomy. Which definitely reduces your tank’s attractiveness and makes it less pretty.

The brown or yellow coloration is caused by a compound called tannins. The famous aquarium décors, driftwood, and bogwood are notorious since they leach tannins into waters.

Other tannins sources are dried leaves and sometimes the tap water itself (only in some places). The compound is harmless to your fish, but it lowers the pH levels and also makes your tank look dirty.

Solution & Prevention

Driftwood and bogwood will leach tannins if you haven’t soaked or boiled them before adding them into the tank. A way to clear your water again is to take those decors out and clean them.

You can easily fit small driftwood in a pot and boil them. But with larger ones, you will have to soak them for three to 7 days in a container. You can add ½ cup of aquarium salt per gallon of water to help the process. Replace with new water when you notice that the color of the water already looks tea-stained. And once the water stays clear even after soaking the whole day, the driftwood is ready to go.

If you have dried leaves on the substrate to create a more natural vibe but don’t want the black water, sadly, you will have to take them out. But if you’re fine with it, then you can keep the leaves. Fun fact, some fish species can actually thrive from tannins in the water!

In addition, you can use an activated carbon filter to remove the tannins and make your tank water clear again. This is also a very good way to fight tannins if you have large driftwood or bogwood in store. That’s because bigger driftwood will continue to release tannins even if you’ve soaked it for a long time.


In some cases, cloudy water is actually not as bad as it seems. Although we still agree that it doesn’t look pretty at all.

But no worries, the ways to get rid of the discolored water and turn them clear again are mostly not very difficult. So don’t panic when you see your tank water gets foggy.

By knowing the causes of what makes your tank cloudy, you can then fix the problem. As we all know, knowledge is key in this hobby.

Hopefully, this article gives you some insight about a cloudy tank and can get you ready anytime the fuzzy water happens to you. Feel free to share your experience with us in the comment sections!

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