Cloudy water can have several causes and depending on the cause, there is usually a corresponding cure. There is no magic bullet solution for cloudy water, it does take a little investigative work to come up with a solution. Based on the color of the water and the circumstances leading up to the appearance of cloudy water, you can usually find the root cause.
In new aquariums, dust from the gravel, if it was not thoroughly rinsed before use, can turn the water cloudy. After a day or so in a new aquarium, bacterial blooms can also make the water appear cloudy, until the beneficial bacteria settle onto a surface to grow. If too much food is added to the aquarium, not only will the dissolving food make the water cloudy, but new bacteria growing to consume the extra nutrients will make the water cloudy.
Using a water test kit to measure the ammonia and nitrite levels will help determine if they are high, which will cause bacteria to grow. Too much light, phosphate or nitrate can lead to green water: an explosion of algae growth. If the filter becomes too dirty it will lose its filtering capacity and the water may become cloudy. Water changes, cleaning the filter, increased filtration, and commercial chemicals added to precipitate suspended particles in the water will all help make the water clear again.
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