Cloudy Tank Water

Why is the Water in my Aquarium Cloudy and How Do I Fix It?



If you wake up one morning to find the water in your tank has suddenly gone cloudy you may be tempted to perform a water change in hopes of remedying the problem. When this method doesn’t work, it would be wise to delve deeper in the cause of the cloudy water. Once you understand what causes the water in an aquarium to become cloudy you will be able to take the necessary steps to correct it. You will also be better equipped to avoid a recurrence of the problem in the future.

Causes of Cloudy Water

Cloudy tank water can be brought on by several different things but the most common cause is a bacterial bloom. Similar to algae blooms, bacterial blooms happen when the population of bacteria in your tank suddenly skyrockets, resulting in a cloudy appearance in the water. The most common cause of a bacterial bloom is excess organic waste build-up in the tank substrate. This may be a result of overfeeding, having too many fish in the tank or adding fish before your tank has properly cycled. Algae blooms can also cause cloudy water but they typically discolour the water, turning it green or brown, rather than making it cloudy. The causes of algae blooms are similar to those for bacterial blooms, largely consisting of excess nutrients like nitrogen and phosphorus as well as too much light or carbon dioxide in the tank.


Another possible cause for cloudy tank water has to do with your tank substrate. When you bring commercial substrate home from the store it is likely to be somewhat dirty – tainted with a build-up of dirt and dust. If you do not rinse the substrate before adding it to the tank, these substances will be released into the tank water and could cause it to become cloudy. To prevent this from happening, be sure to carefully rinse all new substrate before adding it to your tank. Pour the substrate into a large plastic bucket or colander and rinse it with warm water until the water runs clear.

Remedies for Cloudy Tank Water

While you may be able to find chemical remedies for cloudy tank water at your local pet store, you should be wary of using these products. Chemical solutions often do no more than cover up the symptoms of cloudy tank water – they may not actually solve the problem. The first step you should take toward remedying the cloudy water in your tank is to test the tank water for a chemical imbalance. Compare the results of this test to the readings that are normal for your tank – if any of them are significantly different than usual, that may be the cause for the cloudy water. If you determine that the cloudy water in your tank is a result of a chemical imbalance, take the necessary steps to correct that imbalance and the water should clear up.


If you are able to determine that the cloudy water in your tank was caused by a bacterial bloom, the best course of action is to vacuum your tank substrate. By vacuuming your substrate you will be removing accumulated wastes which provide bacteria with the nutrients they need to grow. Once deprived of these nutrients, the bacteria should begin to die and the water should clear up. To keep this problem from happening again it is wise to keep waste build-up under control in your tank. Vacuum your substrate and perform a water change on a weekly basis to remove wastes and to refresh the tank water. You should also avoid over feeding your fish because whatever your fish do not eat will end up sinking to the bottom of your tank. Another important element in preventing cloudy water is adequate filtration – be sure that the filter you are using in your tank is of the appropriate size and that is it functioning properly.