Authored by Douglas Mefford in Pets 
Published on 04-07-2009

Keeping a fish tank is an organic process, which makes keeping the tank water clean and pristine a real task. Cloudy water will often develop in your tank and has to be dealt with to keep a healthy functional display of fish. The problem of cloudy water can happen even before you have a fish in the tank so getting to know what causes this and how to treat the various reasons cloudiness may develop.

While not exclusive, there are two main reasons for a newly filled tank to develop cloudy water. Gravel residue is a primary culprit in new tanks. Anytime you are getting material to put in your tank, be it new or second-hand, you should wash and dry it thoroughly. Gravel especially will have dust clinging to it that will float loose into the water. It may eventually filter out through normal operation but does cut down the life of your filter dramatically.

In a similar vein, the water you use for your tank may already have a number of dissolved particulates in it. Phosphates, silica and heavy metals are the most prevalent culprits. You can determine if this is the problem by checking the pH of the water. If it reads a high alkaline level, treat your aquarium water with a softening conditioner.

At any time after the aquarium tank has been set up, be it weeks or months, the problem of cloudy water may occur again. Most commonly a “bacterial blossom” will be responsible. It is not just the fish that are alive in the environment. Microorganisms flourish within the tank that feed on rotted vegetation as well as excess, uneaten food. A change in the temperature or light intensity can cause these microorganisms to hit a sudden growth spurt and take over a fish tank seemingly overnight.

Maintaining a good filtration system in your fish tank will usually prevent this from happening. Partial water changes also help keep the bacterial colonies from becoming too prevalent. If some of the debris in the water continues to create problems despite filtration, it may be due to them being too small to filter out. In this case you would need to add “water clarifiers” which force the detritus into larger clumps that can be removed by the filter.

Excess algae growth will cause the water to cloud up with a distinctive green tinge due to the chlorophyll in the plant cells. Usually there is a combination of reasons for algae to suddenly go through a rapid growth expansion. As with almost any plant, too much sunlight will cause it to grow. Moving the fish tank or aquarium to a less brightly-lit location may help. Keeping up with the amounts of phosphates and other nutrient minerals in the water will also help you catch an algae bloom before it happens.

Routine water changes can help, however, if the water you use for this is the source of high levels of phosphates you will need to treat it before using it to change the water in the tank. Nitrates are a byproduct of fish fecal matter and will, as expected, increase with time. Keeping the water filtered, changed regularly, and your tank population at a sustainable level will slow down the incidence of this type of cloudiness.