Guide · Vacation setups
Power outage while you're away
When the power cuts out, the filter and air pump stop moving the water surface. What a battery-backup air pump and a check valve can cover, and what they can't.
Short answer
When the power goes out, the filter and air pump stop, and with them most of the water movement at the surface where oxygen enters. A battery feeder keeps going; mains equipment does not. A battery-backup air pump can keep some surface movement going for a maker-stated number of hours, and a check valve stops water siphoning back into a pump that has stopped. Neither is a guarantee for your fish.
What stops and what keeps going
| Equipment | During an outage |
|---|---|
| Filter on mains power | Stops, so the return flow stops breaking the surface |
| Air pump on mains power | Stops; water may siphon back toward it unless a check valve or its position prevents it |
| Lights on a timer or smart plug | Off; what happens when power returns depends on the model |
| Battery feeder (AA cells or built-in battery) | Keeps feeding on its own power |
| Battery-backup air pump | Switches to its battery, if it has one |
Heaters and other life-support equipment are outside what this site covers. If your tank depends on one, ask an aquarium professional how to plan for an outage.
Why surface movement matters
Oxygen gets into tank water mostly at the surface. A 2020 study of 54-liter aquariums found that oxygen uptake from the air was strongly influenced by water flow and by how much open surface was available.[1] That is one lab study, not a universal standard, but it explains why a stopped filter matters.
The filter does more than clean. Tetra says its Whisper power filter adds oxygen by breaking the water surface as it returns water, like a waterfall.[2] An air pump helps the same way: Aquarium Co-Op says bubbles create water movement and surface agitation, which is key to gas exchange.[3] The bubbles and oxygen guide explains this in more detail.
Battery-backup air pumps: what the maker states
A battery-backup pump runs on mains power and switches to a built-in battery when the power fails. Aquarium Co-Op says its pump does this automatically.[4]
| What Aquarium Co-Op states | Figure |
|---|---|
| Battery life, current units | About 20 hours continuous, 40 hours in Power Save[4] |
| Battery life, units sold before August 1, 2024 | About 8 and 16 hours[4] |
| Flow settings | Five adjustable levels[4] |
| Cord | Over 11 feet, with a USB connector that can also run from a USB power bank[4] |
| Shipping | Not available to Hawaii or Alaska[4] |
These are the maker's runtime figures, not an independent measurement, and they do not say how long any tank's fish will be fine. Power Save cycles the air on and off, so it trades airflow for hours. The maker also notes that its printed manual may still show the older figures. The battery-backup air pump guide covers runtime claims and lithium battery care.
Stop back-siphoning before you leave
When an air pump stops, water can run back down the airline. Aquarium Co-Op says its pump should sit above the water level to prevent back-siphoning, and that a check valve must be used if the pump sits below it.[4] Tetra advises a drip loop and an in-line check valve, or placing the pump higher than the tank.[2] Danner says its check valves are marked with the flow direction and go in the airline outside the water, to stop water siphoning back into the pump in a power outage.[5]
See air pump above or below the tank and which way a check valve goes.
A short outage plan
- Fit a check valve on every airline from a pump that sits below the water line, and check its direction.
- Decide on backup aeration. If outages are common where you live, a battery-backup air pump is the documented option; read its runtime as the maker's figure.
- Give the sitter one job for an outage: check the tank once the power returns, confirm the filter and pump have restarted, and call you.
- Know your timers. Whether a smart plug restores its last state after a cut is model-specific; TP-Link does not state it for the Kasa EP25P4. Use lights and other noncritical loads on smart plugs.
Next
Questions
What happens to my fish tank in a power outage?
Everything on mains power stops, including the filter and any air pump, so the water surface stops moving. A 2020 lab study found that oxygen uptake from the air depends strongly on water flow and open surface area.[1]
How long does a battery-backup air pump run?
Only the maker's figures exist. Aquarium Co-Op states about 20 hours continuous or 40 hours in Power Save for current units, and 8 and 16 hours for units sold before August 1, 2024. No independent runtime measurement was found.[4]
Why do I need a check valve for a power cut?
When a pump stops, water can siphon back down the airline into it. Danner says its check valves, installed in the airline outside the water, stop that from happening in a power outage.[5]
Can a battery-backup pump run from a power bank?
Aquarium Co-Op says its pump has a power cord over 11 feet long with a USB connector that can also run from a USB power bank. That is the maker's statement for its own pump.[4]