Why Does My Fish Tank Filter Stop Running?


The filter is probably your most important piece of aquarium equipment. If you discover that your filter has stopped working properly, it is vital to figure out the cause and correct the problem.

An aquarium functions properly in a contemporary home.
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The filter removes or neutralizes wastes and aerates the tank’s water. If either one of these functions is interrupted, you do not have long--probably a few days at most--before the changes will begin to affect water quality and your pets’ health.

A clean aquarium filled with colorful goldfish.
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A variety of signs can tell you that your filter is not working. Sometimes parts of the system will make unusual noises. Maybe the water flow is more or less than average. Many filters use air pumps--you may not see the usual stream of bubbles, or the pump may be ominously quiet. The first place to start looking for a problem is to check for mechanical failure.

The mechanics of an aquarium air pump.
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Look over the system to make sure that it is still hooked up correctly; connections can slip over time or become dislodged. See if any parts are loose. Check whether a plug has been knocked from an outlet. If you use an air pump, examine all parts of the pump and air-tube connections.

If everything is hooked up correctly but the filter will not operate, it may have become clogged. Look for blocked tubing or dirty airstones. If you have an undergravel filter, siphon the gravel using a gravel vacuum. If it’s a filter that uses media such as a power or canister filter, check the cotton floss or filter insert for pieces of waste stopping up the system; rinse out if needed.

Yellow fish swim over gravel at the bottom of a tank.
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If your filter is running but you can tell it’s not quite doing its job because the water is cloudy or smells bad, you may have what is called a "bacteria bloom," where bacteria suddenly spikes to high levels due to buildup of waste. Try a 30-percent water change and also clean the filter by siphoning the gravel or rinsing filter media. Make sure that there is not something stuck in the aquarium somewhere rotting, such as uneaten food, dead fish, dead plants or something that fell in. Also, review your system’s water temperature requirements, and the amount of fish you have for possible overcrowding issues. If none of these correct the problem or it happens over and over, use a testing kit to determine if some kind of imbalance in the water chemistry has occurred.

Goldfish swim to the surface of an aquarium.
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Be familiar with your system so that you know when something abnormal is happening. Perform regular fish-tank maintenance including daily visual checks to verify everything is operating well. This will enable you to catch some problems before they even happen, and to address system breakdowns early, before they do too much damage.

A parrot fish swims in an aquarium.
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