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Troubleshooting an Overflow Box in an Aquarium

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An aquarium overflow box works as an insurance policy, protecting your most vital and expensive aquarium equipment from damages that could occur during a power outage. In the event of a power outage, an aquarium overflow box will ensure that water doesn’t short circuit your filter or air pump. In the event that an aquarium overflow box fails, you’re at high risk for both flooding and fire. It’s important to regularly inspect your overflow box, to ensure it’s working correctly.

The Parts of an Overflow Box

Familiarizing yourself with the parts of an overflow box will help ensure you can pinpoint an problem should one occur. An overflow box is attached to the side of your tank. One basket sits in the water, while the other stays relatively dry on the other side. Connecting the two sides is a U-tube or siphon tube. The siphon tube is a common cause of overflow box failure. Another is the return pump, which sits in the water basket and is used to push water.

Inspecting an Overflow Box

Inspect your U-tube or siphon tube daily. Look around and inside the tube to ensure no blockage or algae buildup is present. About once every other week, inspect your screens and plumbing to ensure they’re clean and free of clogs.

Troubleshooting Microbubbles

The most common reason for overflow box failure is microbubbles. These bubbles will form inside the U-tube, rendering it useless. Do a daily check to ensure that your U-tube is clear of microbubbles. Do this by placing your hand over the opening. If bubbles accumulate there, you likely have a buildup of microbubbles. You can eliminate a microbubble blockage by cleaning the tube.

Troubleshooting Blockage

If your overflow box has stopped functioning, it’s essential to check for a blockage. Algae or fungus may be growing in one of the tubes, such as the U-tube or return pump. Even fish and substrates can cause a blockage, by becoming lodged in the overflow box. Inspect the screens and plumbing. If there’s a blockage, dismantle the blocked parts and clean them thoroughly before reassembling.

Troubleshooting Pumps

Sometimes a pump is the reason an overflow box does not work. If the pump is operating slowly or it’s too small for your aquarium, it’s going to cause the overflow box to malfunction. Oftentimes this is noticeable after the first installation. If a pump is too small it won’t work from the start. If the pump worked fine in the past but suddenly slows down, you may need to prime the pump to get it working again. Fill both the pump and the return tube with water to prime the pump.