Why is my fish tank cloudy?

Cloudy aquarium water is one of the most common problems in fishkeeping. There are many reasons why your fish tank may be cloudy.

It may cause harm to the fish in our fish tank. Changing the color of the water can tell us that there is a problem. Cloudy water is most often a consequence of the multiplication of protozoa. It often appears in a new, immature aquarium. However, a long-standing problem suggests that the cause may be quite different. It can take some time to diagnose and fix a cloudiness caused by certain chemical reactions.

If your brand new fish tank is cloudy, even when there’s no fish inside it, there are several reasons for that.

This guide discusses many different reasons why your tank may have turned cloudy, and explains how to solve the problem.

Key Takeways:

• Cloudy aquarium water is common, often in new tanks due to protozoa growth.
• “Bacterial bloom” can occur but is part of tank maturation.
• Live plants help prevent cloudy water.
• To clear it, avoid chemicals, clean the tank, change water, and adjust feeding.
• Prevent cloudiness with proper filtration, careful feeding, and tank maintenance.
• UV sterilizers can clear cloudy water.
• Brown/yellow water may result from driftwood or leaves; clean and change water.
• Clear tanks enhance the aquarium hobby experience.

What types of cloudy water we can see in fish tank?

• White / gray cloudy water
• Brown / yellow cloudy water
• Green cloudy water

Cloudy water in a new fish tank is associated with the growth of protozoa, it is completely normal. New tanks may turn cloudy because the water hasn’t cycled fully. 

During the maturation period in the fish tank, the protozoa will be gradually eaten up by other organisms in your tank.

We do not change the water, do not clean the filter, do not move the substrate or put the fish in while our fish tank is cycle.

How long cloudy water lasts in a newly set up fish tank depends mainly on the size of the fish tank. The larger the aquarium, the longer it takes to get rid of cloudy water from the moment the filter is switched on (see table).

*It is only an approximate time. Many different factors affect the maturation time of an aquarium.

White / gray fish tank water

White water in the fish tank is associated with the intensive multiplication of protozoa. Cloudy fish tank water makes it hard to see the plants or fish inside the tank.

Bacterial bloom is the main cause

This “bacterial bloom” is a threat to fish tank. The growth of protozoa in the fish tank can limit oxygen, which can lead to the death of some fish. The term “bacterial bloom” also refers to when a new biological filter system is maturing and working at optimal levels.

Cloudy water in the fish tank will limit the plant’s access to light, and this can cause their death. Proper filtration of the fish tank and regular water changes is one of the most effective methods for bacterial bloom. 

Cycle the fish tank naturally

Don’t be disappointed if you notice that your new tank has turned cloudy after just a day.

In the newly established fish tanks, there is an intensive growth of beneficial bacteria that oxidize ammonia and nitrites. Cloudy water may also occur during this process. Let the fish tank pass this cycle naturally. Ammonia and nitrite levels should be tested at this time – once a day or every two days.

Changing the water at this time will not bring any results. In a few days, the water will become cloudy again. This is because fresh water provides nutrients to our fish tank, which are food for cloudy water bacteria. During the cycle, we should not clean the filter or replace the media filter. The beneficial bacteria in your tank can die for several reasons, including changing water conditions.

It’s very easy to kill all the beneficial bacteria in your tank. Changing water conditions are one of the reasons the beneficial bacteria in your tank die.

Live plants

Having live plants in your fish tank will help prevent the buildup of unhealthy microbes, so your fish won’t be affected by any cloudy water.  An increase in nutrients in a newly set up fish tank may contribute to the growth of heterotrophic bacteria. They break down fish faeces, uneaten food and dead plant parts into ammonia. We may also notice a slimy biofilm on the decorations in the fish tank, which can cause cloudy white water.

What are the main causes of cloudy white water in an aquarium?

• A tank where fish are introduced into too soon after being cycled,
• Inappropriate decorations, badly washed out elements of the aquarium decoration, fresh wood,
• Inadequate substrate,
• Overfeeding, which leads to increased ammonia and nitrite levels in fish tank,
• Lack of vacuuming gravel, which leads to a large amount of organic debris at the bottom of the tank,
• Biological imbalance after aquarium cleaning (too much water change),
• Too many fish in the tank,
• Lack of or insufficient water change in the tank,
• Poor filtration,
• Incorrectly selected filter,
• Not cleaned filter,
• Switching off the filter – our filter should work 24 hours a day, 7 days a week. Turning off the filter for an extended period of time can deteriorate the water quality, which will contribute to cloudy water. Switch off the filter only when necessary (during cleaning),
• Tap water that may contain heavy metals, nitrates, phosphates and silicates. Hard water is quite common in the United States. The problem of alkaline water can be solved by adding a conditioner or a pH buffer to it,
• Cloudy water immediately after filling a new fish tank is most likely caused by dust and dirt from the gravel. If this happens, empty the tank, remove the gravel and wash it under running water,
• Chemicals or medications

How to remove white water from a fish tank?

When the balance of microorganisms is restored, cloudy water in fish tank should clarify naturally. Try less invasive ways to deal with cloudy water at first. Don’t use chemicals to clear away the cloudiness.

How to fix cloudy water?

• Clean the bottom of the tank from debris and change some of the aquarium water (about 20-30%) in order to lower the nutrients; one of the mistakes aquarists make is exchanging too much water, which disturbs the biological balance in the fish tank,
• Reduce the amount of food you feed,
• If you have too many fish in your fish tank, it is best to invest in a larger tank,
• Make sure that the decorations used are suitable for the aquarium, and if not, remove them,
• Clean the filter in the aquarium water, if the filter is unsuitable then replace it with a new model,
• Use a water additives called flocculates to catch floating dirt particles; you can also add activated carbon to the filter,
• Use ready-made preparations for water clarification available in stores – make sure to choose products that are safe for fish and aquarium plants.

Tips how to avoid cloudy water

Buy matched filter

Adapt the filter to the size of your fish tank. Also, make sure that there is sufficient water circulation in the aquarium. 

Don’t kill good bacteria

Filter cartridges and other filter elements should be washed in fish tank water – tap water will destroy beneficial bacteria in the filter media; do not sterilize them with boiling water either.

Avoid overfeeding

Do not overfeed the fish and avoid situations where food is not eaten and falls to the tank bottom. Adult fish should be fed once or twice a day and the food poured in should be eaten in less than a minute. It is also beneficial to starve the fish once a week and not feed them.

Regularly clean the tank

Regularly vacuum the substrate surface and regularly change the aquarium water (about 20-30% once a week) in order to reduce nitrate and phosphate levels.

Be patient while cycling the tank

It is best to wait 3-4 weeks after setting up the new aquarium before adding the fish.

Avoid sunlight

Place the aquarium away from the window and avoid exposure to sunlight,

Avoid overstocking

It is recommended to reduce the number of fish in the tank or buy a bigger one if there are too many fish in the aquarium,

Remove rooting decorations

All rotting decorations (roots, bark, pieces of wood) should be removed from the aquarium, dead plant parts should also be removed regularly,

Add RO water

It is beneficial to add RO water to the aquarium; RO filters help remove most of the contaminants from tap water,

Seed the tank

The water purification process can be accelerated by adding gravel from a well-established aquarium to the tank; in a newly set up aquarium, we can also use filter cartridges or bio sponges from existing tanks and thus populate the new aquarium with beneficial bacteria,

Test the water

Test the fish tank water regularly. To make sure that your tank is not cloudy from the water conditions, use a water test kit. If the ammonia and nitrite levels are too high, you can take appropriate preventive measures. 

UV sterilizer

Effective in the fight against cloudy water can be the installation of UV sterilizer. It allows us to improve the clarity of the water in a very short time. 

UV kills most protozoa within a few hours.

The UV sterilizer should be selected according to the size of the tank – for every 100 l there should be a power of 5 It is worth purchasing a sterilizer with LED lights. Even if you make mistakes in setting up an aquarium, which are not difficult to do at the start, this device will significantly reduce the risk of cloudy water. 

Brown / yellow aquarium water

Cloudiness of water can also be associated with the release of humic compounds. In such a situation the water takes on a brown color. The shade of the water resembles tea.

Driftwood

Humic compounds are usually secreted by mangrove or driftwood roots. Driftwood can add chemical –  tannins –  to water and change its color to a cloudy brown. If the roots have not been pre-soaked before adding them to the aquarium, then a slight brown water of the tank may occur.

Leaves

The brown color may also be due to the presence of leaves or other organic matter. Dried leaves also leach tannins that will turn the water brown. You have to remove any dried leaves if you want your tank to remain clear.

Japanese roots are commercially available – these do not dye the water brown. The brown coloration of the water is not harmful to your fish, it can even be very beneficial. There are environments known as black waters where brown water is a perfectly normal thing. These environments are usually found in wooded areas without much water flow. Some fish that live in these environments need just such water. 

Brown water can also be caused by substrate turbidity.

How to get rid of brown or yellow water?

• The substrate must be cleaned of dirt,
• Tart of the water needs to be changed,
• It is advisable to use a cartridge made of activated carbon and a cartridge made of density filter wool,
• Avoid overcrowding and overfeeding your fish

If brown water appears, it is recommended to check the pH level. Tannic acids released from leaves and wood can effectively lower the pH level. 

Green water in the aquarium

Green water in an aquarium does not mean anything other than an increased amount of algae. Euglena algae are the cause. Algae cells are always present in the tank, but they only appear when something disturbs the balance of the aquarium.

Avoid overstocking

In an immature aquarium (where there is not enough bacteria), the algae cells can multiply intensively, which contributes to a change in the color of the water, making your tank cloudy. A common cause of a algae bloom is the introduction of a large number of fish into the tank.

The presence of too many fish leads to increased ammonia concentration and aquarium pollution. Problems often arise if fish are introduced into an immature tank. It is advisable to delay the maturation of the aquarium for up to 5 weeks.

What could be the causes of green water?

• Infrequent water changes and filter cleaning,
• Clogged filter,
• Overfeeding of fish and overstocking the tank,
• Carbon dioxide deficiency,
• Exposing the aquarium to natural light source, and illuminating the aquarium for about 10 hours or more,
• Sudden change of lighting, the algae growth is primarily caused by too much light,
• Excessive nutrients (phosphates and nitrates); phosphates can be introduced to the tank together with tap water – it is worth checking the content of phosphates and nitrates in the water before adding it to the tank; using filtered RO water can also be a good solution,
• Improper substrate preparation; primarily applies to garden soil.

How to get rid of green water?

Green water can be removed easily. The main goal is to reduce the phosphate content to the necessary minimum. The first step is to change 40% of the tank water.

Remove dead plant matter from the aquarium. Filter cotton wool should be put into the filter.

It is also advisable to turn off the lighting or completely darken the aquarium for the duration of the treatment. Too long illumination should be avoided.

A UV lamp may also be helpful in prevention and kill algae cells in fish tank. Adding plants to the aquarium can help reduce nutrients and maintain the biological balance.

Avoid using chemicals to remove green water. It’s never wise to add chemicals to your water to make it more healthy. It may have unintended consequences.

In conclusion

I hope this article helped you understand the real reasons behind the cloudy water in your fish tank.

Keeping a tropical tank is both fun and relaxing, and many people enjoy this hobby. To make sure the water in your tank remains clear, consider all of the above tips. This will allow you  to view the beauty of your aquatic life. For someone who loves aquariums, it’s a dream to have clear water in their tank. 

If you have any questions, a tips, or an experience with cloudy water, please leave a comment.