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Fishician®

Power outages: what to protect, in what order

During a power outage, prioritize oxygen and watch temperature closely while protecting filter bacteria. How quickly each becomes a problem depends on the tank and room conditions.

2 min readUpdated September 25, 2026

About this guide

Troubleshooting

By Fishician

Published September 8, 2026

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The short answer

  • Prioritize oxygen and temperature. Get the surface moving with a battery air pump, or scoop water and pour it back in.
  • Slow the temperature change. If the tank is cooling, insulate without blocking gas exchange. If it is overheating, avoid trapping heat. Monitor temperature.
  • Stop feeding, lights off. Less waste, less heat, less stress.
  • Long outage? Move media from a stopped canister or sump into the tank.
  • Restart in stages. Inspect stopped equipment first, then test ammonia and nitrite over the next days.
An LED flashlight and spare batteries in a protective case
A flashlight and spare batteries support an outage kit. Aquarium aeration needs its own suitable backup equipment.Photo: Mini Maglite LED with accessories — A.Savin, Wikipedia · CC BY-SA 3.0. Resized for display.
What to check when power fails
  1. UrgentOxygenThe surface stops moving while fish keep breathing. Faster in warm, crowded or heavily planted tanks.
  2. CheckTemperatureDrifts toward room temperature. How fast it changes matters most.
  3. CheckFilter bacteriaMedia in a stopped canister or sump runs out of oxygen and starts to die.
  4. AlsoPumped equipmentSkimmers, dosers, chillers and top-off stop. A stopped chiller in a warm room matters.

Right now

  • Air: a battery air pump is the cheapest fix. No pump? Pour water back so it breaks the surface, every so often. Steady beats exhausting.
  • Temperature: insulate a cooling tank; ventilate an overheating one while preventing escape. Check with a thermometer.
  • Food: reduce or briefly pause feeding for healthy adults to limit waste. Fry and specialist feeders need an individual plan.
  • Lights: off. They add heat and drive plant and coral oxygen swings you cannot support.

If it drags on

  • Move filter media into the tank, where the water still reaches the moving surface.
  • Maintain aeration and monitor temperature. Use insulation only while needed to limit cooling.

Restarting safely

  1. Inspect stopped canisters and sumps. If the water in them has gone foul, discard it and rinse the media in tank water. Don't pump it into the tank.
  2. Check heaters are at the manufacturer’s required water level before switching on; not every model is fully submersible.
  3. Restore circulation and air first, then heat, then everything else.
  4. Test ammonia and nitrite over the following days. These checks help detect reduced biofilter capacity; adjust feeding to the animals and readings.

Prepare before it happens

  • A battery air pump with fresh batteries, a jug for moving water, a thermometer that needs no power, and blankets.
  • Consider a UPS sized for circulation and air. Fuel-powered portable generators belong outdoors, at least 20 feet from buildings, with exhaust directed away from openings.
  • Review shared failure points: independently controlled heating, backup circulation, and safely installed electrical circuits can reduce some risks but still need testing and a response plan.
  • Inspect equipment as part of your routine. Some failures occur without warning; test the backup plan.

Sources

Each source is listed with the part of this guide it supports.