Cloudy Fish Tank Causes and How To Fix Them (2024 Guide)

Cloudy Fish Tank
Featured Image – PT-0140 – cloudy fish tank
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: April 8, 2024
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We’ve all faced this predicament. Either you’ve overfed, or you’ve been away for a long weekend, and before you know it, you’re confronted with a fish tank that’s become clouded and downright unpleasant to look at.

This can lead to some major health complications for your fish if left untreated. So what exactly was the cause of this cloudy fish tank water in the first place, and what should you do about it? 

If you’ve ever run into problems with cloudy aquarium water, read on for some tips, solutions, and preventative measures.

Article Summary

  • Cloudy fish tank water can lead to health complications for fish and should be addressed promptly.
  • Cloudy water can result from various issues such as overfeeding, bacterial blooms from fish waste or leftover food, new tank syndrome, overstocking, insufficient filtration, decaying fish or plants, and substrate issues.
  • To fix a cloudy fish tank, you should first identify and address the specific cause.

Why Is My Fish Tank Cloudy?

Goldfish in Cloudy Water
Goldfish in Cloudy Water

The answer to this is that cloudy water in your fish’s home can be the result of quite a few potential problems.

It could be that there are too many fish in your tank, or that there has been a bacterial bloom caused by the accumulation of fish waste or leftover food.

Additionally, a new fish tank with green cloudy water could be the result of fresh substrate settling down.

As a general guideline, seeing cloudy fish tank water means that something is amiss and that you need to take action before there are any health effects on your fish, such as ammonia and nitrite levels leading to poisoning.

As you can tell, the cause of cloudy aquarium water can be somewhat challenging to determine. This becomes easier if you have closely monitored conditions in your tank, and have a regular schedule of changing the tank water.

Whatever the reason, there are a few helpful solutions that can help your water recover from something like a bacterial bloom or algae growth that may be causing the cloudy fish tank. If you have a reef tank, having a gfo reactor and a carbon reactor can help prevent algae growth.

Is Cloudy Water Bad For Fish?

In almost all circumstances, cloudy water in your fish tank is bad for the health of your fish.

Whether it be the result of a recent bacterial bloom, substrate being loose in the tank, or excess waste accumulating to the point of becoming visible, cloudy aquarium water is a sign that something is off in your tank.

Effects of Cloudy Water

Health effects such as swim bladder disease, fin rot, and ammonia poisoning, to name a few, are more easily caught in a fish tank with excessive waste.

Water conditions that lower the effectiveness of your fish’s immune system can quickly result in sick or even dead fish as waste and other materials make their way into your fish’s gills.


Even something as seemingly benign as the cloudiness caused by certain area’s tap water can be cause for concern. This may indicate the presence of harmful heavy metals and nitrates, which should be treated with tap water conditioner so that they do not harm your fish.

What Causes Cloudy Water In A Fish Tank?

Cloudy Fish Tank Being Vacuumed
Cloudy Fish Tank Being Vacuumed

As previously mentioned, there are several factors that can lead to a cloudy fish tank. Most of these are avoidable with careful monitoring and planning on the part of the aquarist, but even the most vigilant fish owner may one day see green water pop up in their tank.

New Tank

A new aquarium is always an exciting prospect! You get to plan the fish that will be swimming, decorations, and layout of the whole thing.

But do you often take the time to consider the beneficial bacteria living in your tank?

Here’s a video of a new tank with cloudy water…

Cloudy water is normal in a new tank

Beneficial Bacteria

Beneficial bacterial colonies are primarily responsible for much of the nitrogen cycle in your fish tank. These beneficial bacteria ensure that ammonia levels within your tank won’t rise to toxic amounts and wind up poisoning your fish.

New tanks have an incredibly small amount of beneficial nitrifying bacteria to start with, and can be quickly overwhelmed (referred to as “new tank syndrome”) if these good bacteria aren’t given the proper amount of time to jumpstart the nitrification process.

Nitrogen Cycle

Beginning the nitrogen cycle in a newly established tank can take from about a week to upwards of seven weeks, during which you should be testing the water regularly to ensure that the ammonia level is being kept at safe levels.

Starting with less fish and gradually increasing as your tank can handle more nitrogen will ensure that you have a healthy community for years to come.


One of the main causes of fish disease and dirty tanks, overfeeding happens when we add more food than our fish can eat at any one time during a feeding.

Not only can it cause health problems such as constipation, dropsy, and choking for your fish, it can drastically affect the overall quality of the water.


A good rule of thumb to prevent the hazards associated with overfeeding are to remove any uneaten food after a half hour of feeding. This will keep excess food from breaking down and changing the water quality of the tank.

Uneaten Food

Fish Food
Fish Food

As food breaks down over time, the excessive nutrients that are then free in the water can feed free floating algae and microorganisms in your tank, causing a bacterial bloom. This causes a cloudy, greenish hue to the water, along with a noticeable smell of rotting food and is no good for your fish.

Having extra food break down in their water is somewhat like having rotting food in your bedroom, but imagine being sealed into the room all day and having to eat and sleep in it!

Fish swimming in this cloudy water will have to contend with lowered immune systems and higher rates of disease.

They are simply immersed in potentially harmful bacteria, which is a sure way to have a sick population of fish and other organisms on your hands.


Having too many fish in your tank can cause problems with cloudy water, along with generally being hard to live with for most fish species.

Even schooling fish such as goldfish will begin to feel crowded in cramped conditions, and anti-social fish such as bettas may react with more aggression towards their neighbors.

How to Prevent Overstocking

The best advice for aquarium owners looking to prevent overstocking is to plan ahead when thinking about your tank.

Plan your filter media, substrate, and size of tank around the maximum number of fish you intend to have in the long term, so that you don’t find yourself suddenly needing to move some out in order to make room! Consider investing in a larger tank and filter system if you plan on adding fish in the future.


Additionally, more fish means more waste to attempt to filter out at one time. This can not only overwhelm the beneficial bacteria in your tank, but can quickly spiral into more than your filter media can handle as well.

Insufficient Filtration

Planted Aquarium with Sponge Filter
Planted Aquarium with Sponge Filter

Not having enough filtration within your tank can certainly lead to green aquarium water. The filters in our tank act to remove suspended media such as fish waste and bits of plant from the active flow of water, to be removed upon cleaning. 


Leaving your filter uncleaned for too long can lead to a bacteria bloom, as organisms living on the surface of the filter that would normally be removed have time to proliferate. This bacterial bloom can become noticeable as green water in your tank.

When you have a filter that has become clogged, or simply isn’t powerful enough for the amount of waste in your tank, cloudy water can be a common occurrence. Regular water changes, along with consistent filter maintenance are a great way to keep things from spiraling out of control.

Replacing Filters

By replacing filters regularly (according to the nature of the specific make and model of filter in question,) you can keep bacterial blooms from becoming as common.

Most filters will come with specific instructions regarding when to deep clean them and when to replace specific parts such as filter pads.

Dead fish

Decaying fish in the tank is a sad situation overall, but can become a harmful one for the rest of the aquatic life in your tank if left unchecked.

You should be able to identify a dead fish by its lack of swimming, general bloated appearance, and eventually by the smell it produces. If the fish has been left for long enough, it may even begin to make the aquarium water cloudy as it decomposes.

When in doubt, don’t be afraid to attempt to move the fish if you think it may be dead. Using a soft net or a jet of water from your aquarium filter to gently move it will generally get it to react if still alive and well.

Removing dead fish is a simple enough process, but you’ll want to get your water tested and consider partial water changes after removing the fish. This is because even for a short period of exposure, having a deceased fish in your established aquarium can begin to affect water quality.

Decaying Matter

Leftover frozen food, decaying plants, and dead fish all begin to produce tiny particles of matter as they break down. This can raise nitrate levels, and can potentially overwhelm the nitrogen cycle occurring in your tank if it goes on for too long. 

Consider the use of water changes after noticing dead material in order to remove the tiny particles of dissolved constituents left over. This will help keep ammonia and nitrite levels in your aquarium water from reaching dangerous levels.

Identifying dead plant

It may be somewhat harder to determine whether a plant is dead than a fish, as they neither move nor react when stimulated, but there are some tell-tale signs.

Seeing algal growth on plants, rotting and withering, and general off-coloring preceding a smell are all indicators that something is wrong with the health of your plant and it may need to be removed.


Use a net of appropriate size, rather than your hands when removing dead matter from your tank. The bacteria making up a typical algae bloom can be harmful to human health as well, and avoiding personal contact is important.


Numerous Swimming Goldfish Together in a Tank
Numerous Swimming Goldfish Together in a Tank

Sometimes it may be the surface of the tank itself, rather than the aquarium water that has become cloudy. This may be the result of either the bacteria in your tank, or the substrate along the bottom of the aquarium itself. 

When the heterotrophic bacteria in your tank break down uneaten food, fish waste, or dead materials into ammonia it also creates a sort of slimy biofilm. This film can coat both the inside of the glass and the structures inside of the tank, leading to a clouded, hazy appearance


These heterotrophic bacteria differ from the beneficial nitrogen-fixing bacteria in your tank in that they only break down organic compounds into nitrogen, rather than fixing it further into less harmful states.

If this happens in a new fish tank, you can simply allow the natural process of beneficial bacteria breaking down this nitrogen to occur over time. In a tank with fish in it, you can use water changes and feed sparingly until the cloudiness has subsided.


Substrate refers to the material (sand, gravel, soil, etc.) that you place on the bottom of the tank to provide ground cover, an interesting texture, and a place for your aquatic live plants to root down.

Certain substrates such as sand and soil may naturally become dislodged and float freely in the tank, leading to a cloud of particulate matter. This should either settle back down to the bottom of the tank over time, or be removed by your filtration system.

Using Correct Substrate

While pulling soil or sand from your home garden may seem like a cheap, easy way to provide some substrate for your tank, you may want to think twice.

Some soils can contain harmful chemical pesticides and additives, along with parasites and diseases that can infect your fish!

Some substrates, such as gravel and pebbles, may come coated in epoxy designed for use in aquariums.

This is sometimes pre-rinsed prior to sale but may become dusty in shipping or during storage. After being added to your tank, this dust can mix with the water and lead to a cloudy appearance for your tank. 


Prior to adding substrate to your tank, I recommend giving it a thorough rinse to ensure that all of the dust has been removed. This will keep your tank looking clean and clear, avoiding the mixing of dust and water that creates cloudy water.

How To Fix A Cloudy Fish Tank

Aquarium Glass Getting Cleaned
Aquarium Glass Getting Cleaned

Given that there are a variety of ways your aquarium water can become cloudy in the first place, there are a few recommended ways to fix it and bring your water back to its normal clear quality.

That being said, a good place to start for any issue with water parameters is to start with a partial water change of 10-15%, along with testing the water before and after.

Decaying Matter

If you know that the cloudiness in your tank is from dead fish, no longer living plants, or excess fish waste, the first step is to remove the offending material.

If possible, try to avoid jostling or shaking as you remove them, which can break things apart further and cause more cloudiness.

Along with cloudiness, you will likely detect a smell that only fish can produce when they pass. You’ll want to move quickly to bring things back to normal if you’ve gotten to this level of funk!

After removal, test the water for nitrate levels, pH, and oxygen. Things will likely be a bit high, but the natural cycling process in your tank may be able to take care of things if they haven’t gone too far above 0 parts per million.

If necessary, perform some tank maintenance with a few water changes over the course of a week, testing as you go to ensure that things are changing.

Insufficient Filtration

If you have too many fish for your current filter setup, you’ll likely notice problems with cloudy aquarium water that may indicate that a dangerous poisoning event is close at hand.

You may want to add activated carbon media to help things initially, and then look at a larger or more robust filter system for your tank.

Filter floss can be a great way to keep your filters clean and help them last longer. If the filter you’ve bought from the pet store has a replaceable filter, make sure that you are following the directions regarding maintenance and upkeep!

An undergravel filter, paired with a usual canister filter and airstone can be a great place to start. These all work in tandem to increase water movement throughout your tank, which in turn allows particles to be removed at a greater rate before they have the chance to settle.

Water Color

Aquarium with Algae
Aquarium with Algae

There are a few different detectable colors that you may see if things have changed in your tank, and they may indicate different things going on.

White to gray coloration means something more to do with rocks and dissolved materials, while greens and browns show that there is a bloom of algae or organic compounds are breaking down.

White or Grayish Water

White to gray water coloration can mean that there is leftover fine dust on the surface of the substrate, that a bacterial blossom has occurred, or that there are dissolved constituents floating freely in your tank.

Additionally, your tap water may have excess bubbles of oxygen, or potentially even harmful heavy metals and chlorine that add a color to the tank water.


Using a gravel vacuum to remove any floating particles of dust can help. If you do indeed have an issue with heavy metals, you may need to use the additional chemical filtration of a water conditioner drop.

These bind to certain harmful chemicals such as ammonia and allow them to be safely filtered out of the tank, rather than getting into your fish or plants. 


Performing regular gravel vacuuming will ensure that if there is indeed any leftover dust or small particles that have come loose you will remove them before they have the chance to become an issue.


Additionally, water changes every week or two will help to keep water conditions from reaching the state where you’ll see a bacterial bloom.

Green Water

Green water usually indicates that there is an issue causing extra plants or algae to grow in your tank. This may be because there is too much direct sunlight hitting your tank, excess nutrients in your tank from overfeeding, or that chemicals such as phosphates and nitrates have reached the level where they have caused a bloom.


If the problem is too much light, the fix can be as simple as dimming your aquarium lights, or removing your tank from an overly sunny spot. Using an activated carbon filter and UV sterilizer can help, along with performing a water change to correct any chemical imbalances.


Perform regular water changes! This, along with careful placement out of direct sunlight can help avoid problems associated with algae blooms and help clear cloudy tank water.

Yellow/Brown Water

Why you get yellow water

This color can be the result of tannins being released from wood, or potentially from the presence of too many fish producing waste for your filters.


Removing any recently-added driftwood should halt the release of additional tannins. For overcrowding, consider either purchasing an additional tank or reconfiguring your filtration setup if the size of tank is not the issue.


Pre-soak any wood prior to adding it to your tank.

In addition to removing any potential tannins, you’ll also want to ensure that any harmful bacteria or parasites on board don’t make it into your tank! As for overcrowding, plan your tanks carefully! Talking to your local fish store can be a great way to create a long lasting, mature aquarium.


Why is my fish tank cloudy after a water change?

If you’re seeing cloudy water immediately following a water change, it is likely the result of heavy metals or chemicals in your tap water.

New water should not have the chemicals of your old tank water, so in this case you would want to consider either using pre-filtered reverse osmosis or RO water or the use of a water conditioner.

How long does it take for cloudy aquarium water to clear?

You should begin to see changes in water clarity within 1-2 days. If, after this point the water returns to its cloudy state or gets worse, perform another water change and take a look at your filters to ensure that they are performing properly.


Throughout today’s article, we’ve looked at some of the causes, effects, and how to fix cloudy aquarium water. While seeing green or brown water can be distressing, it’s important to note that the effects are not often immediately fatal and with quick action and planning towards prevention you can keep conditions in your tank healthy for years to come.

Feel Free To Share!

I hope that you’ve enjoyed this post on keeping your tank clean, and that it has helped answer any pressing questions you may have. Feel free to share this post with any other fish fanatics that you may know, and I wish you the best of luck on your continued aquarium hobby adventures.

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