Understanding Aquarium Overflow Boxes


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 an aquarium overflow box fails, you’re high risk for both flooding and fire. It’s important to regularly troubleshoot 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 issue should one occur. Troubleshooting begins with knowing how to identify common issues with certain parts of the overflow box. 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 reason for overflow box failure. Another common reason for failure is the return pump, which sits in the water basket and is used to push water.

Inspecting an Overflow Box

Regularly expecting your overflow box will ensure that you’re able to pinpoint problems, before the tank overflows. Inspect your U-tube or siphon tube daily. Look around and inside the tube, to ensure there’s no blockage or algae buildup. 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. Inspect your u-tube daily to ensure that they’re clear of microbubbles. Do this by placing your hand over the opening. If bubbles accumulate there, you likely have a build-up of microbubbles. You can eliminate a microbubble blockage by cleaning the u-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 the return pump. Even fish and substrate can cause a blockage, when they become logged in the overflow box. Inspect the screens and plumbing. If there’s a blockage, dismantle the blocked parts and cleanse 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 successfully prime the pump.

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