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Power cuts and house moves are two of the most stressful moments for any fishkeeper. In both cases, the same three things keep your fish alive: oxygen, stable temperature and protecting the bacteria in your filter. With a little preparation, most aquariums come through a power cut of several hours, or a move across the country, without losses.
Part 1: What to do in a power cut
The first hour
- Don't panic. A well-stocked tank has enough oxygen for at least a few hours, and the water holds its temperature for longer than most people expect.
- Don't feed. Food uses oxygen as it's digested and adds waste the filter can't process.
- Insulate the tank. Wrap blankets, towels, duvets or polystyrene around the sides and over the lid (leaving a small gap for air) to slow heat loss.
- Switch off equipment at the wall so a power surge doesn't damage it when the electricity returns.
Keeping oxygen up
Oxygen is the most urgent concern, especially in warm, heavily stocked or marine tanks. Without a filter or air pump moving the surface, oxygen levels gradually fall.
- Use a battery-powered air pump if you have one. It's the single best item to keep for emergencies.
- If not, scoop out a jug of water and pour it back from a height every 15–30 minutes to agitate the surface.
- Watch for fish gasping at the surface, a sign that oxygen is running low.
Reef keepers with EcoTech VorTech pumps can keep flow running in an outage with a battery backup; the Fused VorTech Battery Backup Cable connects the pump to a suitable battery.
Keeping the temperature stable
Tropical tanks lose heat slowly when insulated, often only a few degrees overnight. Tropical fish tolerate a gradual drop to around 20–22°C for a short time far better than a sudden change. If the cut is long:
- Float sealed bottles of warm (not hot) water in the tank, replacing them as they cool.
- Chemical heat packs such as the ProRep Heat Pack can be wrapped and placed against the outside of a small tank under the insulation.
- In summer, the risk is overheating instead. Keep curtains closed and don't insulate.
Monitor the temperature with a digital thermometer such as the Fluval 2-in-1 Digital Thermometer.
Protecting the filter bacteria
Beneficial bacteria need oxygenated water flowing over them. In a filter that stops for more than a few hours, especially an external canister, the water inside becomes stagnant and the bacteria start to die.
- If the power is off for more than three or four hours, open canister filters and either remove the media into a bucket of tank water with an air stone, or keep it wet and exposed to air.
- When the power comes back, don't just switch a stagnant external filter on. It can flush a slug of toxic water into the tank. Empty and rinse the canister in tank water first.
After the power returns
- Check every piece of equipment has restarted, including heaters, filters, pumps and controllers.
- Test ammonia and nitrite over the following few days. Some bacteria loss is common.
- If ammonia appears, do a water change and dose a detoxifier such as Seachem Prime, then add bacteria such as Seachem Stability or Dr Tim's One & Only. Our guide to lowering ammonia and nitrite explains the steps.
- Feed lightly for a few days.
Be prepared: an emergency kit
Keep these together in a cupboard, ready for storm season:
- A battery-operated air pump with spare batteries, airline and an air stone.
- A digital thermometer.
- Blankets or polystyrene sheets cut to fit your tank.
- A few clean water containers, such as the 25 Litre Container or 10 Litre Container.
- A dechlorinator and a bottle of live bacteria.
A standard mains air pump such as the Eheim Air or Oase OxyMax can also be run from a small UPS or portable power station during an outage. Browse our air pumps.
Part 2: Moving house with an aquarium
Before moving day
- Stop feeding 24–48 hours before the move to reduce waste in transit.
- Do a water change a couple of days before so the water is in good condition.
- Gather sealed containers, fish bags, an insulated box (a cool box works well), nets, buckets and towels. A fine net such as the Aqua One Fine Fish Net makes catching easier. See our fish nets.
- Plan to set up the tank first at the new home, before the furniture.
On moving day
- Save tank water. Fill clean containers with as much of the existing water as you can carry, so you can refill with water the fish are used to.
- Catch and pack the fish last. Bag them with one-third water and two-thirds air, or move them in a lidded bucket with tank water. Keep them dark, insulated and upright.
- Keep filter media wet. Put the media in a sealed container of tank water. This is your biological filter; don't let it dry out or rinse it in tap water.
- Empty the tank completely. Never move a tank with water or substrate inside; the weight can crack the glass or break the seals. Bag damp substrate separately.
- Move the empty tank carefully, supported along its base.
At the new home
- Place the tank on a level, strong cabinet, away from radiators and direct sun.
- Add the substrate and decor, then the saved water, topping up with new water treated with a tap water conditioner.
- Reinstall the filter with its original media, plus the heater, and let the temperature stabilise.
- Float the fish to match temperatures, then release them gently. Keep the lights off for the first day.
- Test the water daily for a week and dose bacteria if ammonia or nitrite appear.
Marine and reef tanks
Reef tanks need more planning. Move corals in containers of tank water, keep rock wet in tubs, and prepare plenty of new saltwater at the new house in advance. Keep heaters and pumps running in containers if the move takes longer than a few hours. Expect a mini-cycle afterwards and test carefully before adding new livestock.
When to ask for help
If your aquarium is very large, or you're moving a long distance, consider rehoming fish temporarily with a friend or local store. If you'd like advice on planning a move or putting together an emergency kit, our team is happy to help.
