How to Prevent Aquarium Sump Overflows

Prevent sump overflows during a power outage

Aquarium in the dark
Aquarium in the dark. Markus U./Flickr/CC BY-SA 2.0

Saltwater and freshwater aquarium sump pumps are a great innovation and a terrifically useful piece of aquarium system equipment. However, they do have one a drawback and it's something you may not have thought about until it's too late. Since the sump pump is powered via the electricity in your house, if there is a power outage, the sump pump will stop working.

What Happens When the Power Goes Out

Once the sump pump stops pumping and the tank water level has dropped to the overflow level, the tanks will continue to drain into the sump pump via the pump outlet in the tank.

If your pump nozzles are even 3" below the water surface, they can suck a lot of water from your tank into your sump. This will lead to a sump pump overflow, a leak on your floor, and potential damage to your home.

A Simple Test to Determine If Your Tank Is at Risk of an Overflow

Perform this test to determine if you have a potential problem with your sump pump. It is very easy and will only take about 10 minutes. You'll need to gather these tools prior to starting the test:

  • Bucket or another water container
  • Water scoop (a coffee cup works fine)
  • Drill motor
  • 1/8" drill bit

Step by Step Guide to the Test

  1. Have a bucket and scoop standing by, near the test location.
  2. Top off your sump pump to your maximum "normal" level while the tank is running.
  3. Turn off all water pumps and skimmers in your tank.
  4. Watch the water level in your sump as it rises.
  5. If the water level starts to go above approximately 1" below your sump rim, start removing water into the bucket to keep it below that level.
  1. If the sump water level doesn't go above that point, you are fine.
  2. If you had to bail water, turn the pumps back on and mark the water level in your sump when everything is running normally. This is your "maximum fill" sump water level during normal operation.

If you had to lower the sump water level during the test, there are a couple of simple solutions:

  1. Don't fill your sump above the "maximum fill" mark.
  2. Unplug the return pump in the sump and raise the pump nozzle above the water in the aquarium.
  3. Drill a small (1/8") hole in the side of the pump nozzles, just below your normal tank water level.
  4. Perform the above test again to make sure that the problem has been solved.
  5. Adjust the "maximum fill" mark on your sump.
  6. Once you are confident that your sump will not overflow, even during a power outage, you should sleep a bit better knowing that you won't wake up to a wet floor in the morning.

Additional Aquarium Tips

Stay informed and learn more about how to keep your aquarium running when the power goes out to help you prepare for an emergency. Your fish rely on electricity to keep them alive and you'll need a plan should there be a prolonged power outage.

If you did use the tips and created the hole in the nozzle, it's important to periodically check to make sure that the hole you drilled in the side of the nozzle is not clogged with debris. If you do find that it is clogged, inserting a toothpick in the hole will usually keep it open and working properly.

To help avoid overfilling your aquarium system when topping off, consider installing an automatic top off system.

These systems not only help prevent accidentally putting too much water in the system when topping off, they also take the drudgery out of having to periodically haul water from your faucet to the tank and pouring it in. The DIY automatic tank or sump top off project is easy to complete, the components are easy to find, and relatively inexpensive to purchase.