Why Does a Fish Tank Filter Bubble So Much?

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Once you've set up your aquarium and installed the filter according to the instructions, you might see some bubbles coming out of the filter. Air bubbles in a fish tank are not necessarily a bad thing. A fish tank filter bubbling is a sign that the filter is working. Also, tiny bubbles forming on live plants, called pearling, is a sign that the plants are healthy and producing oxygen.

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A fish tank filter bubbling is a sign that the filter is working.
Image Credit: mtreasure/iStock/Getty Images

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However, if the filter is producing excessive amounts of bubbles or if the bubbles are very large, this could mean there's an issue with your aquarium filter. The cause of excessive fish tank filter bubbling is usually a dirty, broken, or clogged filter. If the aquarium filter is not working correctly, your fish might not be swimming in breathable water.

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Function of aquarium filters

Fish tank filters are necessary for tanks because they help purify water and keep your fish tank colonies healthy. Your fish are "breathing" in the water that is in the tank, and the cleaner the water, the better for the fish. Most fish tank filters use air to pump, or circulate, the water through the tank.

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A calm, steady stream of air forces water through the fish tank filter where plant matter, excess food, rot, waste, moving sediment, and sometimes chemicals are removed or trapped. Therefore, regularly cleaning the filter is important. The filter essentially aerates the water, creating some visible air bubbles.

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Excessive fish tank filter bubbling

A functioning aquarium filter should create some bubbles. These air bubbles actually help add oxygen to the water. When air bubbles rise to the surface and pop, they release small amounts of oxygen necessary for the fish to breathe in the water. However, excessive fish tank filter bubbling can cause some problems, though nothing too serious.

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If you have screens of bubbles that obscure your view of the fish or create significant air currents, this can be unpleasant for both you and your fish. Also, if too many air bubbles are accumulating on the surface of the water like a sheet, you have too many bubbles and possibly too much oxygen in the water. Excess oxygen or nitrogen (though most likely nitrogen) can cause blisterlike swelling to form around the face and eyes of fish, a condition commonly called "bubble disease."

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Common causes of too many bubbles

The most common cause of excessive fish tank filter bubbling is a dirty filtration unit. When a lot of waste — especially proteins, such as uneaten food — build up in a filter, it can cause clumps of bubbles and even foamy masses to appear. Clearly, cleaning the entire filtration unit including all tubes and components is the solution. If there's too much buildup in the tank, it will likely require an entire-tank cleaning, which is yet another good reason not to overfeed your fish.

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Old or clogged components can also be a source of filter issues. If there's a clog in one part of the filtration unit blocking airflow, the air will be forced through another spot, creating excessive bubbles. Sometimes, cleaning all mechanical components can help, but often, some or all parts need to be replaced. Sponges and foam pads specifically need to be changed regularly.

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Errors causing aquarium bubbling

The novice aquarium owner might make two mistakes that can cause excessive fish tank bubbling. First, hanging filters should not be too high. These are aquarium filters that fit on the side of the tank and allow water to cascade into the tank. There should be no splashing.

Second, never clean the tank with soap, even dish soap, or any detergent. This is true of fish tank filters too. Soap is very difficult to rinse entirely, and even the smallest amounts can cause bubbling or can be poisonous to the fish.

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