The direct answer when the power stays off
Aquarium fish survive a long power cut on surface exchange, so keep the water's surface moving and the fish's oxygen demand low: a battery-powered air pump with an airstone is the best tool, hand-stirring or pouring tank water back from a jug is the no-equipment fallback, and feeding stops completely until power returns. A still tank is not an instant emergency — a lightly stocked aquarium coasts for hours — but every hour of stillness and warmth narrows the margin, so start gentle aeration early rather than waiting for fish to gasp.
Why oxygen fades in a silent tank
In a running aquarium, the filter's return and any airstones constantly renew the thin surface layer where oxygen enters the water. When the power cuts, that renewal stops, the fish and the filter bacteria keep consuming oxygen, and the surface layer is used up first. Warm water holds less oxygen than cool water, so a summer outage drains the tank faster, and a crowded tank with large fish drains it faster than a sparse one. The filter itself becomes a secondary problem over a long cut: its bacteria starve in the dark, which is why keeping the media wet matters for the restart.
The first hour: aerate and reduce demand
Fit the battery air pump and airstone to your most crowded or warmest aquarium first, because that tank's oxygen falls fastest. For tanks without a pump, stir the surface with a clean hand or whisk every so often, or dip out a jug of tank water and pour it back from a height so it splashes and folds air in. Lift or prop the lid open for gas exchange if the room is safe and the fish are not known jumpers, and dim your own activity around the tank — fish that rest quietly use less oxygen than fish being peered at and startled hourly. Feed nothing, however appealing the begging looks; digestion raises oxygen demand and uneaten food consumes more as it decays.
Holding the line through a long outage
Rotate the manual aeration in short, regular sessions rather than exhausting yourself in one long effort, and prioritise the hours around dawn if the cut runs overnight, when plant and algae respiration adds to the drain in planted tanks. Keep the aquarium insulated and the room temperature steady — a tank cooling slowly is far safer than one you try to warm with candles or hot water bottles pressed to the glass, which also risk cracking it and polluting the air around an open lid. If you must change water, change a modest portion with dechlorinated water matched closely in temperature, poured in from a height so the change itself aerates.
Restarting safely when power returns
When the power returns, check each aquarium's fish before celebrating: normal swimming and breathing mean the routine worked, while fish still gasping at the surface need the restored filter plus extra aeration for a while longer. Rinse nothing in tap water, confirm the filter actually restarted — some stall after outages — and test the water over the following day, because the starved filter may let ammonia creep up. Feed lightly at first, not a celebration feast. Fish that remain listless, pip at the surface, or show red gills after conditions normalise should prompt advice from an aquatic veterinarian. Scheduling the stirring rotation and battery swaps in KinsLe Care Teams means nobody in the household has to guess when the last oxygen round happened during the next outage.