Why Is My Fish Tank Cloudy – Reasons and Cures

cloudy fish tank
Care & Maintenance

Why Is My Fish Tank So Cloudy After a While?

Many aquarium owners are baffled by the exact same problem – “Why is my fish tank cloudy”?. There is no single cause to this problem. But the problem can be pinpointed to some basic causes based on color and circumstances of the cloudy water appearance in your aquarium.  Below we look at some of the reasons why you get cloudy water and some possible easy to do solutions

Grayish or White Water

Gravel Residue
Gravel Residue

Gravel Residue

When you fill the tank and the water becomes cloudy within an hour or two, this is because the gravel is not sufficiently washed. To resolve the problem, drain the tank. Then rinse the gravel until the water becomes clear.

Dissolved constituents

Washing the gravel might fail to resolve the cloudy water problem. Therefore the next possible cause of cloudy water in a tank that has just been filled is a high level of dissolved constituents. These are such as silicates, phosphates, or heavy metals. If you do an acidity test of the water, it is likely to be alkaline PH. Treat the water with conditioners to resolve the issue.

You can also use Reverse Osmosis to resolve the issue and add more benefits. You can buy it from a fish shop or buy units that you can use to make Reverse Osmosis water.

Bacterial Blossom

Sometimes, water will not become cloudy immediately the aquarium is set up. It will appear months, weeks or days later. When this happens, the cause of the cloudy water is usually bacterial bloom. When a new aquarium undergoes the initial break-in cycle, the water gets a little hazy or cloudy. It takes many weeks to many months to determine colonies of bacteria that are able to remove waste from the aquarium water. The cloudiness should disappear after a while.

Excess food that fish don’t eat or decaying plants also causes the cloudy water seen in bacterial bloom. Bacterial blooms are easy to resolve. To resolve the bacterial bloom issue, keep the aquarium very clean. Remove the debris like uneaten foods and decaying plants to clean it. Also vacuum the gravel frequently and do partial water changes. Ensure to reduce feeding to every third or second day, this will decrease decay of excess food.  Another point to note is the types of fish you have in your tank, knowing what breed they are and feeding them with the right amount of food is very important

Sometimes it might be hard to remove debris using vacuuming and water changes. Use a flocculent to clear the particles away. Flocculates make debris particles to clump together. The debris can thus be removed easily by the filter. Flocculates can be found at your local fish shop and they are usually marketed as water clarifiers.

Green Water

why is my fish tank cloudy
Greenish Water Tank

Green water is caused by algae growth. It is very hard to remove algae from water but you can easily cure it if you know the cause. The primary causes of green water are:

Excessive lighting

This is the easiest cause to cure. Exposing the aquarium to direct sunlight or leaving the lights on for a long time will lead to the growth of algae. Decrease the exposure time of the aquarium to lighting and move it indoors away from direct sunlight.

Excess nutrients

Nutrients like nitrates and phosphates also support the growth of algae. These nutrients must be reduced to stop algae growth. Changing water will remove the algae from the water but the problem will still be there. It is vital to battle nitrates and phosphates at their source so that you eradicate them completely.


There are two sources of phosphates. The sources are decaying water like fish food and water source. Testing tap water for phosphates will determine if you have an issue with the source of your water. In the case that your water has phosphates in high levels, you will have to use a phosphate remover or Reverse Osmosis for water treatment. Also, reduce the food amounts that you use to feed your fish. You can change to a brand of fish food that is lower in phosphates.


Nitrates rise in the aquarium water naturally over a period of time as a result of fish wastes. You can remove the nitrates by changing the water. Ensure your filter is clean and enough for the size of your tank. Also, do not overcrowd the fish because you will regularly fight high levels of nitrates.

Many cases of cloudy water can be resolved by changing water, using great quality of fish food, and keeping the gravel clean. With the above understanding of cloudy water causes and cures, next time when you hear aquarium owner say “why is my fish tank cloudy” then you are better equipped to give them advice & fish care tips.

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