Why You Have A Cloudy Fish Tank (And How To Fix It) (2023)

A cloudy fish tank is something that no aquarist wants to see. Not only is it unsightly, it could also be dangerous!

However, many owners don’t know the first thing about clearing up cloudy aquarium water. In fact, most don’t even know what the cause is in the first place.

But that’s not surprising when you look at the fishkeeping buyer cycle. It’s really not their fault!

Here’s why:

When they run out and get a new fish there are a million things to think about. Care requirements, necessary purchases, where to put the tank in their home, you name it!

It’s a lot.

But nowhere in that process is there a point where someone stops them and explains the potential causes of cloudy water (and what to do about it).

And that puts these owners in a tough spot when it happens to them. They’re on the clock and fighting from behind!

But not on our watch. This guide will go over everything you need to know about the causes of a cloudy fish tank, and how you can clear things up.

This way when the time comes, you’ll be ready!

Table of Contents
  1. Why Is My Fish Tank Cloudy?
  2. White/Gray Cloudy Water
    1. Likely Causes
  3. Green Cloudy Water
    1. Likely Causes
  4. Yellowish-Brown Cloudy Water
    1. Likely Causes
  5. Conclusion

Why Is My Fish Tank Cloudy?

Cloudy aquarium water can be an alarming sight for fishkeepers! Most aquarists go to great lengths to keep tanks clean and water conditions stable.

So when that otherwise clear water starts to look murky and discolored, many go into a mild panic!

But first, it’s important to understand that there isn’t a single cause for cloudy water. Many factors can affect water quality. Some issues are benign while others can be a sign of something more serious going on.

Any to figure it out, you’ll need to identify the type of water you’re dealing with.

You can encounter three different types of cloudy aquarium water. These include white, green, or yellowish-brown.

(Video) How to Fix Cloudy Water in an Aquarium! (Quick and Easy)

Understanding the differences between these cloudy issues can help you take action and make changes to prevent future cloudiness problems from occurring.

White/Gray Cloudy Water

This is a pretty common type of cloudy water in new fish tanks that were established very recently (sometimes within one day).

The severity of the problem can vary quite a bit. In some cases, the issue is nothing more than a slight haziness.

Many people don’t even realize the cloudiness at first. Instead, some think it’s just dirty glass!

In more severe cases, your fish tank can be overtaken with a thick opaque haze! In these instances, the water can look as thick as milk.

So, what causes a white or grey cloudy fish tank?

Likely Causes

1. There are a couple of culprits for this type of cloudy water, and the simplest is residue from your substrate material!

Gravel is usually coated in a fine layer of dust that you need to remove before adding it to your tank. If you don’t do that, the aquarium tank water will cloud up immediately. The dust will float through the water before eventually settling.

The problem can persist for several days depending on your tank setup. If you have a filter, the system can remove the fine particles.

However, this usually takes several days.

In the meantime, the water return spout will constantly kick up the particles and prevent them from settling!

Author Note: Even if the residue has time to settle, you should always aim to remove it. Movement from your fish will just make the cloudiness return later.

2. Another likely cause to investigate is the condition of the water you used.

For example, hard water is pretty common in the United States. This water usually has dissolved constituents, which could include everything from metals to minerals. There could also be phosphates and silicates in your water supply.

Have you ever taken a moment to look at the water after you fill up a glass from the tap? For many homeowners, the water will appear foggy before clearing up a bit. When you’re filling up a massive aquarium, that cloudiness is only intensified!

(Video) How to Fix Cloudy Water in an Aquarium (Easiest Method)

Use a test kit to analyze your water supply. It will likely be high up on the hardness scale and have a higher pH balance.

3. Finally, the most common cause of cloudy water is a bacterial blossom.

Before you start worrying, this blossom can actually be very beneficial. When you first set up a tank, the water must go through a nitrogen cycle.

This establishes those all-important bacteria needed to clear waste from the closed environment. These bacteria will turn fish waste into nitrates, making the water a lot less harmful for your fish.

Bacterial blossoms can occur several weeks or even months after setting the tank up. You might also experience cloudiness after a major water change.

Treatment & Prevention

How you’re going to treat this issue depends on the cause. If residue from your substrate is to blame, take some time to clear things up. You can use a gravel vacuum or store-bought water clarifier. There’s also the option of letting your filtration system do the work for you (if you have a good one).

To avoid this problem in the future, clean out the substrate thoroughly. Use a sifter or fine-mesh sieve to rinse off any residue left behind.

To address cloudiness caused by dissolved constituents, you’ll need to improve your water supply. You can use a reverse-osmosis filter to get rid of any contaminants before you add it to your tank. Alternatively, you can use a water conditioner.

Finally, there’s the issue of bacterial blossoming. There’s actually nothing you have to do to get rid of this issue. Your cloudy fish tank should clear up in about a week!

Author Note: However, if you want to take care of the problem quicker, you can perform a partial water change. This usually stops blossoming in its tracks.

You can also prevent future issues by removing debris and keeping the tank clean at all times.

Green Cloudy Water

Green cloudy water is an unsightly issue that can quickly overtake an aquarium. The good news is that the problem isn’t particularly harmful to fish.

The bad news is that it can take some time to get under control!

Likely Causes

If you’re dealing with a green cloudy fish tank, it’s most likely caused by algae overgrowth!

Aquariums are the perfect environment for algae to flourish. In just the right conditions, this growth can quickly overwhelm the closed habitat.

(Video) Cloudy Water in a New Fish Tank

This isn’t the same type of algae that’s clinging to the glass, it’s phytoplankton. This type of algae is so tiny that you can’t see it with the naked eye.

Author Note: Phytoplankton is a single-cell organism that suspends in water, which is what’s causing the foggy effect.

So why are this algae all of a sudden going crazy in your tank? Well, it could be due to the location of the tank or the condition of the water.

If your aquarium is located in direct sunlight, you may be inadvertently feeding the phytoplankton too much! More than about 10 hours of light can cause the algae to grow and spread at a rapid pace.

The water in the tank may be supporting the algae as well. Excess nutrients like phosphates and nitrates are food sources that help algae thrive.

There are ways to address the extra nutrients in the water. But, it’s something that’s going to take some time to fully get under control.

Treatment & Prevention

Some algae in your aquarium is fine, but too much of the stuff will make your fish’s home look filthy!

The best way to address the problem is to simply limit light exposure.

Start by putting your tank lights on a timer. They should be on for no more than eight to ten hours a day.

If the tank is close to a window, consider moving it. You could also use some window coverings or apply a light-blocking material to the side of the tank that’s exposed.

To effectively manage phosphate and nitrate levels, you’ll need to change the way you take care of the tank. For immediate relief, do a partial water change. This will reduce some of the cloudiness quickly.

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

Take a look at your filtration media. Chances are, it’s covered in grime! When the filter is unable to catch contaminants, the phosphate and nitrate levels in the tank will rise naturally. Oftentimes, simply replacing the filtration media will do the trick.

You can also be more proactive about removing messes from the tank. Limit feedings to only a few minutes and remove any excess food from the habitat. Get rid of dying plants and any other biological matter that could sour the water.

Author Note: You can also increase the frequency of your water changes. All of these small tasks should help to keep phosphates and nitrates to a minimum, which will stunt the growth of phytoplankton.

Yellowish-Brown Cloudy Water

The last type of cloudy aquarium water you’ll encounter is yellow or brown. Again, the severity of this problem can vary widely based on the cause.

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In severe cases, your fish tank could start to look seriously discolored, which would be a cause for concern. In other cases, the issue could be something as simple as staining from your decor!

Likely Causes

In the worst-case scenario, water could become brown or yellow due to overcrowding. No matter how small your fish are, they still produce waste.

One big mistake newer fishkeepers make is overcrowding the tank to create a schooling effect. While many species will naturally group up, there still needs to be some open space.

The more open space there is, the harder it is for waste to sour the water. When you overcrowd fish into a small tank, ammonia and nitrite levels will go through the roof.

And this isn’t just a cosmetic issue.

These contaminants will chemically burn a fish’s gills. This will result in a very painful death!

But it might not be all bad.

If you have a well-maintained tank that’s still filled with cloudy brown water, the issue might be caused by staining rather than contaminants. Driftwood and decaying leaves produce a substance called tannin.

The tannins are organic and completely safe for your fish. In fact, many freshwater fish in the trade come from blackwaters that are very rich in tannins. Depending on the species you have, the tea-stained cloudiness could even benefit your fish!

Treatment & Prevention

To get rid of yellow or brown staining, you need to reassess your tank setup. Do some research to figure out how much space each fish in your aquarium needs (start with our library of care guides).

But realize that there’s no exact science when it comes to this.

Generally, larger fish need more room because they produce a lot more waste than smaller fish. Consider investing in a larger tank or purchasing multiple tanks to prevent overcrowding.

For staining caused by tannins, you’ll need to remove the source. You can get rid of tannins in driftwood by presoaking them. This won’t remove the existing tannins in the water, but it will prevent the problem from getting worse.

To help clear up a cloudy fish tank, invest in a carbon filter. Carbon filtration will remove the tannins and make your water crystal clear again!


As you can see, there are a ton of potential causes for a cloudy fish tank. But a lot of them aren’t that bad!

The most important thing is to educate yourself and take action when you notice something you don’t like. Even better, engage in good care to prevent this from happening in the first place.

(Video) Bacterial Bloom And Cloudy Water - The What, Why and How to Fix it (SIMPLE)

Just like anything, it’s always easier to stop a problem from happening than it is to solve it. Be consistent, follow our recommendations above, and your aquarium water will be clear in no time.

If you have any suggestions on ways we can improve this resource we would love to hear from you. Our whole mission is to provide the most helpful information possible, and we’re always open to getting a little extra help!


Why You Have A Cloudy Fish Tank (And How To Fix It)? ›

The most common cause of this is overfeeding your fish. Not only will your fish poop more, but there will be uneaten fish food source rotting at the bottom of the tank syndrome – fix this by cutting back feedings and removing all the uneaten excess food and decaying excess waste from your tank.

How do you clear a cloudy fish tank fast? ›

Add activated carbon media to the filter, whether loose or carbon pads. Adding activated carbon media or activated carbon pads to the filter will help clear the water and adsorb nutrients that feed the bacteria bloom.

Why is my fish tank cloudy and how do you fix it? ›

The cloudiness you are experiencing is probably one of two things. First, overfeeding your fish can cloud your water as the uneaten food is allowed to decompose. At each feeding you should feed no more than what your fish can eat in one to two minutes. Overstocking the tank (too many fish) also can cause cloudy water.

Why is my fish tank cloudy but chemicals are fine? ›

The cause is usually due to bacterial bloom. As the new aquarium goes through the initial break-in cycle, it is not unusual for the water to become cloudy or at least a little hazy. It will take several weeks to several months to establish bacterial colonies that can clear waste from the water.

How long does it take for a cloudy tank to clear? ›

This is normal when an aquarium is first set up. It is referred to as a bacteria bloom. The cloudiness should be gone within anywhere from two days to a couple of weeks. You can do a 10 to 15 percent partial water change and gravel vacuuming after a week to speed it up.

What products to use for cloudy fish tank water? ›

Tetra Water Clarifier clears cloudy aquarium water caused by over feeding, gravel dust and other minute suspended particles. This phosphate-free liquid solution is safe to use in all freshwater aquariums. This effective formula works by causing small, suspended particles to quickly clump together.

Can fish live in a cloudy tank? ›

In some cases, cloudy water can be harmful to fish, but not all the time. Here's what you need to know about cloudy water in an aquarium. There's a break-in period for all new aquariums, and this is when most aquarists will see the first instance of cloudy water.

How do I fix cloudy water in my aquarium after water change? ›

Clear Cloudy Aquarium Water: Removing Organic Materials

The better way to deal with cloudy aquarium water is to remove excess organic materials that are causing the bacterial bloom. First of all, remove excess uneaten fish food, dead fish or dead snails and dead or dying aquarium plants.

Does cloudy water mean ammonia? ›

CLOUDY WATER = HIGH WASTE (Ammonia / Nitrite) + LOW BENEFICIAL BACTERIA (Nitrosomonas sp. / Nitrobacter sp.) It can be assumed that, if the water was to be tested, the test would show that waste (toxic Ammonia & Nitrite) is present in the water.

Should I clean my fish tank if it's cloudy? ›

The solution is simple: do nothing. Don't add a UV sterilizer or do lots of water changes to remove the haziness; this just makes the bacterial bloom last even longer. Instead, wait one to two weeks, and the water will gradually clear up on its own as the bacteria reestablishes itself again.

Why is my fish tank cloudy but no fish? ›

If the tank is very new, and you don't yet have any fish (so the tank has not yet started to cycle), then a white or gray cloudiness is likely due to some piece of decoration or equipment not being thoroughly rinsed with cool running tap water prior to introducing it to the tank.

What is the best crystal to put in a fish tank? ›

Rock crystals such as Quartz (including Rose Quartz, Smokey Quartz, Apricot Quartz, etc.), Jasper, Citrine, Jade, Ametrine, Tiger's eye, Amethyst, Agate, Black Tourmaline, and Petrified Wood are all considered safe additions to your aquarium.

What is the best water for a clear fish tank? ›

If you want to be sure your aquarium water is free from mineral and chemical contaminants, deionized water is a great choice. Deionization is ineffective against bacteria, but it does filter some contaminants that even reverse osmosis systems cannot catch.

Why wont my cloudy tank go away? ›

It's usually caused by one of three things: microscopic debris in the water that the filter can't remove, minerals leaching from décor and substrate in acidic water conditions or a bacterial bloom.

Why won't my tank stop being cloudy? ›

This can be caused by: Overfeeding – the bacteria feed on uneaten food in the aquarium. Overcrowding – too many fish for the volume of the tank. Poor filtration – not enough filtration for your size tank and/or number of fish.

How do you clean a cloudy glass tank? ›

Lay the tank down on a towel, and pour enough vinegar on the affected glass to cover it. Let it sit for 10 to 20 minutes, then scrub with a non-abrasive pad or cloth. If you have a stubborn patch of build-up, try using a razor blade or algae scraper to gently scrape the scale away from only glass panels.

Does cloudy water bother fish? ›

Though cloudy water isn't always harmful to fish, it certainly can be. You should take steps to clear up your tank's water as soon as possible. As you will see, some of the issues that cause an aquarium to turn murky are symptoms of greater problems.

What happens if you put too much water clarifier in fish tank? ›

The only exception is if you add too much water clarifier. If this is the case, your water clarifier is going to go on a clumping spree and will very likely turn your water a cloudy brown color. If you use one of our top picks, an overdose should be harmless and sort itself out in a few days.

Why is my water cloudy? ›

The cloudiness is due to tiny air bubbles in the water. Like any bubbles, the air rises to the top of the water and goes into the air, clearing up the water. The water in the pipes coming into your house might be under a bit of pressure.

Do fish go to sleep? ›

While fish do not sleep in the same way that land mammals sleep, most fish do rest. Research shows that fish may reduce their activity and metabolism while remaining alert to danger. Some fish float in place, some wedge themselves into a secure spot in the mud or coral, and some even locate a suitable nest.

How long does bacterial bloom last? ›

Bacteria Bloom (cloudy water) will occur 2 to 4 days after fish are added to the tank. The cloudiness, caused by initial bacteria growth, is not harmful to tank inhabitants, and will clear on its own. Have patience! If your water does not clear after 10 days, consult with your Aquarium Adventure Fish Specialist.

Can tap water have ammonia in it? ›

Ammonia may be present in drinking-water as a result of disinfection with chloramines. The presence of ammonia at higher than geogenic levels is an important indicator of faecal pollution (5).

Is cloudy water OK? ›

Cloudy tap water is usually safe to drink. Most of the time, cloudy water is caused by harmless air bubbles or mineral buildup in the water. Before drinking cloudy tap water, you should do a couple tests to see how the water acts once the water settles in your cup.

Can I just add tap water to my fish tank? ›

Municipal/Tap Water

Most municipalities treat drinking water with either chlorine or chloramine for disinfection purposes. Chlorine is extremely toxic to fish and needs to be completely removed before the water comes in contact with fish. Chloramine is chlorine bonded to ammonia, both of which are detrimental to fish.

Can you do a 100% water change fish? ›

Completely replacing the water in the fish tank is a bad idea because it will remove beneficial bacteria that live in the tank and reset the nitrogen cycle, which could kill your fish. If you regularly clean your tank, doing a partial water change is the best option.

Where do you put fish when cleaning a tank? ›

Use a small bowl, mug or cup that has been thoroughly rinsed with distilled water as a temporary tank. Never place fish in containers that have been washed with soaps, as even a small amount of residue can be toxic. In a pinch, you can also use a large plastic zip bag.

What does bacterial bloom look like? ›

If you have a bacterial bloom in your aquarium, the water becomes cloudy and turns milky within a few days. The clarity of the water is significantly reduced, but no floating particles are visible to the naked eye.

Should you put rocks in your fish tank? ›

Rocks and wood provide a great deal of surface area for the nitrifying bacteria to colonize on. These bacteria help to eradicate ammonia and nitrites from your aquarium – important since both of these substances are toxic to fish. ?

What Colour stones are best for a fish tank? ›

Dark gravel colours can enhance bright fish colours and black substrates can look striking, contemporary and attract less algae than light substrates.

Should I put pebbles in my fish tank? ›

Aquarium pebbles are the most common aquarium substrates over all kinds of fish tank stones and sand. This is not only for decorating your fish tank, but there are sundry bio-chemical properties in gravels, that help filtrate your aquarium, and provide nutrients to the fish and other inhabitants.

Can I put fish in cloudy water? ›

In some cases, cloudy water can be harmful to fish, but not all the time. Here's what you need to know about cloudy water in an aquarium. There's a break-in period for all new aquariums, and this is when most aquarists will see the first instance of cloudy water.

Why is my fish tank cloudy but no ammonia? ›

Heterotrophic Bacterial Blooms

Heterotrophic bacteria become a problem when their population grows rapidly to feed on high levels of organic materials dissolved in the water column. This sudden heterotrophic bacteria growth is known as a bacterial bloom, causing white cloudy aquarium water.

How do I add good bacteria to my fish tank? ›

Good bacteria can come from a handful of populated gravel or substrate, or a used filter pad that's been rinsed in tank water, a used sponge filter, or even an external filter box. Dropping a piece of used filter pad into a new filter box helps establish a colony of good aquarium bacteria in a new tank.

Why is my overfed fish water cloudy? ›


Feeding your fish too much and too often in itself can cause water cloudiness. This may be due to food particulates dissolved in the water, a bacterial bloom, or both. The instructions on many fish-food containers tell you to feed multiple times per day.

How do I keep my fish tank clean without changing water? ›

Vacuum the Gravel Fish feces, shed scales, uneaten food, dead bits of plants, and other debris will settle to the bottom of your tank. Vacuuming the gravel every week will remove much of this debris and refresh the tank, brightening the gravel and keeping the tank healthier.

What does a bacterial bloom look like in a fish tank? ›

If you have a bacterial bloom in your aquarium, the water becomes cloudy and turns milky within a few days. The clarity of the water is significantly reduced, but no floating particles are visible to the naked eye. This fact enables you to exclude turbidity due to floating detritus and dust.

Will bacterial bloom clear up on its own? ›

This is called “bacterial bloom.” This cloudiness is caused by initial good bacterial growth and is not harmful to your fish. It will clear up on its own. As you will see, you need this bacteria growth for a healthy aquarium.

How long does it take for a bacterial to go away? ›

The duration for which the Bacterial Infections may last usually depends upon the type of bacteria causing it as well as the severity of the infection. Usually, 10 to 14 days or more are the expected time duration for the symptoms to persist in case of Bacterial Infections which are a result of secondary infections.


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