In a power cut, keep water moving first: oxygen runs low without pumps. A battery air pump or battery-backed wavemaker is the most useful kit you can own. Then protect the temperature by insulating the tank. Bulk Reef Supply says a tank can manage two to three days without filtration, heating or lights if the water keeps moving.
The first hour
Bulk Reef Supply puts water movement first, because without pumps, gas exchange drops.
- Start a battery air pump or a battery-backed wavemaker
- No backup? Stir or scoop the water by hand every so often to move the surface
- Don’t feed: food adds waste and uses oxygen
- Unplug equipment so it doesn’t all restart at once when power returns
If it lasts longer
Temperature becomes the issue as the hours pass. In winter, wrap the tank in blankets or sleeping bags to hold heat. In summer, keep the room shaded.
Bulk Reef Supply’s holiday guide says temperature becomes a threat after about 24 hours without power. Check it regularly with a battery thermometer.
When the power comes back
Restart the return pump and wavemakers first, then the heater. Watch the skimmer: it may overflow when it restarts, so start it last or empty the cup first. Check temperature and salinity, and test ammonia if the outage was long.
Kit worth having
Bulk Reef Supply ranks the options. It says every tank should have battery backup for at least one wavemaker. Then come inverters, then battery air pumps, which it says will usually keep a nano going. A generator suits large, valuable systems. A power monitor that sends an alert to your phone tells you there’s a problem while you’re out.
Test your backup every few months. A battery that won’t hold a charge is no help on the day.
Common questions
How long can a reef tank survive without power?
Bulk Reef Supply says two to three days if the water keeps moving. Without movement, much less.
Should I feed my fish in a power cut?
No. Food adds waste while filtration is off.
What’s the cheapest backup?
A battery air pump, which Bulk Reef Supply says will usually keep a small tank going.
Sources and limits
Last checked 13 October 2026. This guide brings together the published advice below. It can’t see your tank: if livestock is in distress, act first, then ask an experienced local shop or club, ideally with your test log to hand.