The two risks in a cherry shrimp power cut
A power cut threatens cherry shrimp through falling oxygen and drifting temperature, not through hunger or darkness. Without the filter running, the water stops moving, the surface film thickens, and the shrimp's grazing world slowly suffocates, especially in a warm room where warm water holds less oxygen. A heater going off matters more slowly, since a tank cools over hours rather than minutes, but shrimp stressed by one problem cope worse with the other. Your whole response is about buying time calmly on both fronts.
Oxygen first: air, surface, and stillness
Oxygen is the first job for cherry shrimp when filtration stops. If you own a battery-powered air pump, run it with an airstone on a gentle setting, because rising bubbles break the surface and drive gas exchange in still water. Without a pump, stir the surface softly with a clean cup or jug every so often, pouring tank water back in from a small height to ripple it. Then leave the colony alone: stop feeding entirely, since uneaten food consumes oxygen as it decays, and resist lifting plants or decor to count shrimp, because chasing them around a dark tank burns the very oxygen you are trying to save.
Holding temperature steady without power
Temperature during a cherry shrimp power cut is managed by slowing the drift, not by chasing a number. Wrap the tank in towels, blankets, or a sleeping bag, covering the top as well, since an insulated small tank cools or warms far more slowly than a bare one. Keep the room door closed and curtains drawn against either cold or hot sun, depending on the season. Never pour hot water into the tank or float bottles of it, because a local hot spot beside cold water is a sharper shock to shrimp than a slow, even slide across the whole tank.
What to watch while you wait
Watching cherry shrimp during an outage tells you how urgent things are. A colony still grazing slowly over plants and moss is coping, even if it is quieter than usual. Shrimp gathering at the surface, clustering around the airstone's bubbles, or lining up near the waterline are signaling low oxygen, and that is your cue to stir the surface again or add a second air source if you have one. Shrimp lying still on their sides across the substrate is the serious end of the scale; improve aeration as best you can and prepare to act the moment power returns, rather than attempting a large water change in the dark with untreated water.
When the power comes back on
When power returns, a cherry shrimp tank needs checking before it needs feeding. Confirm the filter actually restarted, since some filters lose their prime and hum without moving water, and rinse nothing yet. Test for ammonia once the lights are back, because the filter's bacteria may have thinned during a long stoppage, and do a modest partial change with temperature-matched, treated water if the reading is not zero. Skip the first feeding if the outage was long, and watch the colony across the next day for delayed losses before deciding all is well. For step-by-step help in the moment, KinsLe's Kimmy can walk you through the restart checks in order while you stand at the tank.