Why Is My Fish Tank Cloudy? How To Fix Cloudy Fish Tank Water

Is your fish tank always cloudy?

Cloudy fish tank water is a common problem and it can be caused by any number of things that we’ll cover below.

Sometimes it’s an issue of having an overstocked tank – you might need to take some fish out. It could be due to overfeeding or a malfunctioning filter. Cloudy water can even be caused by tank additions like driftwood.

Let’s find out why the water in your aquarium is cloudy along with how to fix it.

Cloudy Fish Tank Fixes

how to fix cloudy water in fish tank

Regardless of how long the system has been running, the nitrogen cycle is almost always to blame for cloudy water.

In brand new fish tanks, it’s a good thing, and completely normal.

First off, let’s explore the biome of the home aquarium.

Fish, like all organic life, produce ammonia.

In constructing a home aquarium, whether it’s a small 3-gallon tank, a 55-gallon fish tank, or something much larger, our goal is the same: to achieve a stable and healthy ecosystem.

For this to occur, we need to get our nitrogen cycle in order.

The first step in becoming a successful aquarist is to understand the nitrogen cycle.

The Nitrogen Cycle

cloudy fish tank
Source: How the nitrogen cycle affects cloudy fish tank water

Nitrogen-consuming bacteria are the soul of the fish tank biome.

Fish waste, rotting food, and all other organic waste generated in the tank produce ammonia.

At high levels, ammonia is extremely toxic and is one of the leading causes of aquarium fish death.

Here is how the nitrogen cycle works, and how it can lead to the cloudy fish tank water.

1. A particular variety of bacteria, called Nitrosomas, lives in our tanks.  This bacteria converts the ammonia caused by waste in the tank, into the less toxic ‘nitrite‘.

2. Another form of bacteria, called Nitrobacter, consumes the nitrite, and converts it into ‘nitrate‘. Nitrate is the least toxic byproduct that we need to manage in our home aquariums.

3. Nitrate is fairly innocuous but can become toxic at high levels. Nitrate is removed by water changes. The populations of these bacteria must be sufficient to handle the nitrogen load of the fish tank.

How To Avoid A Cloudy Fish Tank

When starting a new aquarium, it’s very important to “cycle the water” before adding fish.

This can be the first mistake many people make, understandably eager to get their new hobby started.

Water cycling is vital to a beautiful, healthy fish tank, and is a fairly straightforward process.

The purpose and process of cycling are to allow the population of nitrogen-consuming bacteria to build up gradually in preparation to break down the toxins naturally generated in the tank by fish waste.

The best way to prevent issues, cloudy water included, is to get a healthy start.

A great strategy when first starting out is to set up your tank in its entirety before you even think about getting fish.

For example:

  1. Make sure that the tank is in the exact location that you would like since once it’s full of water, moving it becomes quite the ordeal
  2. Rinse any gravel several times in a bucket until it runs clear, then add it to the tank
  3. Add your heater (unless this is a cold water aquarium), filter, filter media, lights, and accessories
  4. Plug everything in, add some water to the filter box, and start the system

This will result in the least amount of shock to your new fish as well.

Test Your Fish Tank

why is my fish tank always cloudy

Before adding any fish, use this time to ensure that everything is working correctly:

  • That the temperature remains steady
  • The filter runs well
  • That any air pumps or water features are performing as they should

Of course, there will be a brief period of cloudy water in a new fish tank after you add water to gravel.

As the gravel settles into place after being stirred up, the water will clear up.

Once the dust has settled, add a bit of fish food. Within a few days, you will see cloudy water.

This is a good sign!

It’s called a bacteria bloom.

This is the bacteria growing in your gravel and filter that will keep the tank stable throughout its lifetime. The first bloom is ammonia-consuming bacteria.

This will settle and you may see two more bouts of cloudiness before the water clears again and remains that way: this process takes an average of two weeks.

Add Your Fish

cloudy water in fish tank

Now it’s time to add some fish!

Add the hardiest fish first, and only a couple at a time.

The general rule is 1 inch of fish per 10 gallons at a time… So if you have a 20-gallon aquarium, add 2 small 1” (or 4 half-inch) fish at a time.

In a tropical community tank, a pair of platties or mollies are ideal, but this is your aquarium so of course, it’s up to you!

To keep nitrate levels in check, the water must be changed. A 10-20% water change per week is a good rule of thumb.

If the water becomes cloudy after fish are added, it is likely due to a bacteria bloom and will fade on its own within 24 hours. If the water remains cloudy after a day or two, then a 25% water change will likely fix the issue.

Also always be sure to change the filter media on schedule. The filter is removing a large portion of waste and debris. If your media is clogged, water quality can quickly deteriorate.

Reasons For Cloudy Water In Fish Tanks

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Here are some other things to consider if you are experiencing cloudy fish tank water.

1. Fish Death

If your fish tank is well established and suddenly becomes cloudy, check for deaths.

Few things cause an ammonia spike as fish loss does and, if not remedied quickly, the issue can snowball and create an increasing deterioration of water quality and continued loss. So act quickly.

2. Over Feeding

Over-feeding is another common cause of cloudy aquarium water.

If there is still food present a few minutes after feeding your fish, then you are overfeeding them.

3. Wrong Nitrate Levels

If no obvious source of an ammonia spike is present, then test your aquarium water to check the ammonia and nitrate levels.

Test strips are readily available at any pet store and online (you can always find them on Amazon).

The API Freshwater Test Kit is a good option as well.

How To Get Rid Of Cloudy Fish Tank Water

how to get clear fish tank water


If nitrate levels are elevated, check that the filter media is fresh and clean.

Change medium as is appropriate, then perform a 25% water change.

Using a double dose of Amquel or a similar ammonia-removing water conditioner can also be quite helpful.

Move décor as appropriate to vacuum up as much waste and debris as possible. If uneaten food or dead fish are found, then you have your answer.

If a water change does not solve the issue, or the cloudiness is severe, a filter additive may be appropriate.

Purigen For Water Cloudiness

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Purigen is a favorite for fixing fish tank cloudiness among aquarium enthusiasts.

It works quickly, and effectively and can be rinsed and reused a couple of times in case of future issues. Many keep a package in the filter just to keep the water polished and consistently as clear as possible.

In a back-hanging filter, simply slip the bag behind your filter cartridge. In a canister tank, use as directed or as you think appropriate.

Some choose to slip it inside or along with the physical filter for polishing, others add it to the biological medium.

Try different options and see which works best for your particular style of filter and circumstance.

Continue to perform 25% percent water changes every 5 to 7 days until the water has cleared.

Why Is My Fish Tank Green?

If your water is cloudy, but with a green hue, it’s likely an algae bloom in your fish tank.

Long term, a great solution is to add live plants to the aquarium. What you can add depends on what type of fish you have (cichlids and goldfish will destroy plants).

The plants fix green algae in a fish tank by diminishing the availability of CO2 in the tank for the algae to thrive on. At the same time, plants generate more oxygen for your fish.

Another option is simply to reduce light wattage or the time that lights are on per day.

A regular light timer works great. Turning the light off completely and covering the tank with a blanket for a week or two will usually kill off the algae initially.

Change the water once a week or as usual and the reduced light will keep this from happening again.

Brown Algae In Fish Tank

If the cloudy water has a brown or yellow hue, it’s usually due to two things: peat moss or decor.

The addition of peat or peat-containing filter additive to reduce ph can cause water to appear brown.

Peat is an excellent natural material to soften water and lower the ph. It can cause discoloration, however. This is temporary and will fade with time and regular water changes.

It’s a bit unsightly, but temporary and will clear itself.

The other cause is the addition of tannin-containing décors, such as aquarium driftwood.

If possible, boil the wood in a large pot until the water runs clear. If this is not an option due to size, then the only solution is either to remove and soak the item or allow the tannins to leach out over time.

This will happen, and though unsightly, it’s harmless to wait for your lovely new decor to “settle”.

Prevent Cloudy Water

To sum up, the best remedy for cloudy water is to avoid the issue with regular maintenance.

Fish tank aquariums require:

  • Require regular water changes
  • New filter media
  • That they not be overstocked with fish
  • That they not be left with excess food
  • Any dead fish must be removed
  • Check nitrate levels

When in doubt?

Do a 20% water change!

If you have a pH problem, this is how to lower the pH in your aquarium (natural methods only).

Thanks for reading, please leave any comments or questions down below.


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