What Happens When You Forget to Turn on the Pump in a Fish Tank?

Aquarium pumps, particularly those in filters, keep aquariums habitable. Pumps provide water movement, which improves oxygenation and gas exchange. Additionally, many aquarium pumps run filters that provide chemical, mechanical and biological filtration. When you lose a pump, you lose this lifeline, and the clock is ticking to get a new pump before the ecosystem is damaged.

  1. Oxygenation

    • Air holds oxygen better than water, which means most of the oxygen in aquarium water comes from the atmosphere around the tank. Water movement improves this gas exchange, removing carbon dioxide and adding oxygen to the water. When a pump fails, water movement decreases. In extreme cases, fish may begin to suffocate. When fish don't have enough oxygen, you may see them "gasp" at the water's surface. The exact amount of time you have before the situation gets dangerous for fish varies considerably based on a number of factors, including the size of the tank, the number of fish and the temperature. Err on the side of caution and replace the pump as soon as possible.

    Nitrogen Compounds

    • Pumps often power filters. Filters remove toxic contaminants like ammonia and related nitrogen compounds. When a filter fails, ammonia and other toxic compounds can build up, poisoning fish. The symptoms of ammonia/nitrite poisoning closely resemble those of low oxygen, since ammonia damages the gills. Fish swim in jerky, erratic motions and gasp at the water's surface. When you lose a pump, you need to replace it quickly to avoid permanently harming the fish.

    Selecting the Right Pump

    • Manufacturers rate aquarium pumps in gallons per hour. For most aquarium applications, a pump needs to have a rating for six times the aquarium's volume per hour. Aquarium filters follow the same guidelines. So a 10-gallon aquarium should have a pump rated at 60 gph. Keep in mind that aquarium pumps have many applications, and a few specialized applications like powering sump filters or DIY protein skimmers need different ratings.

    Skipping the Current

    • In a few situations, a lack of a water pump may not spell disaster. Some fish thrive in the absence of current. For example, the betta requires very weak current, since its long, flowing fins make it very difficult to fight strong water movement. Additionally, baby fish -- called fry -- cannot fight current at all. When you're breeding your fish, stick to filters like sponge filters, which can operate with almost no current, ideal for these applications.