A power cut stops heating, filtration, and aeration at once, and for a white cloud mountain minnow the outage unfolds in a forgiving order. This is a cool-water fish, so the temperature problem that endangers tropical tanks in winter is much smaller: the water drifts slowly toward room temperature, which white clouds tolerate well. The real threats are falling oxygen and the filter bacteria starving while the pump sits silent. Your job during the cut is to slow both processes down with insulation, surface movement, and restraint.
Hold Temperature and Stop Feeding
Wrap the tank in blankets, towels, or spare insulation over the glass and lid as soon as the power fails, leaving no need to open the lid repeatedly, because every opening loses the warm, humid air and heat you are conserving. In a heated room, a white cloud tank may need nothing more than this for many hours. Stop feeding completely for the duration: an unfiltered tank cannot process waste from a meal, and uneaten food decays into exactly the ammonia spike you are trying to avoid. Resist hot-water bottles against the glass for this species; uneven heating stresses cool-water fish more than a slow, even drift toward room temperature does, and if the room itself is bitterly cold, warm the room rather than chasing the tank.
Keep Oxygen Moving Without Power
Oxygen, not temperature, is the clock on a power cut. A battery-powered air pump with a sponge or airstone is the ideal answer and worth owning for any tank; run it in bursts if the batteries must last. Without one, break the surface yourself: scoop tank water in a clean jug and pour it back from a height, or stir the surface gently, at intervals through the outage, and watch the fish for the answer. White clouds crowding the surface and gasping means act now and more often; fish holding calmly in mid-water means your rhythm is sufficient. Keep the lid on between stirrings, keep lights and room disturbance down, and never add unfamiliar chemicals or conditioners in a panic.
When the Power Comes Back
Do not assume the danger ended with the lights. Check that the filter actually restarts, because impellers can stall, and be aware that filter media sitting stagnant for many hours may have lost bacteria or built up waste; rinse media only in removed tank water, never under the tap. Test the water before the first post-outage feed, feed lightly for the next day or two, and watch for ammonia effects such as clamped fins or surface hanging. Inspect each fish rather than just the school, change part of the water if tests are off, and note how long the outage lasted and how the tank coped, while the details are fresh, so the next plan is better than this one.
If You Are Away When It Happens
Outages rarely wait for you to be home, so the routine above needs to exist outside your own head: who nearby has a key, where the battery pump and spare batteries live, and what not to do, including not feeding and not adding hot water. Write it for a non-fishkeeper, in the order events unfold. Write that sheet before you need it, then store the handover where it can actually be used: a KinsLe Care Pass gives the neighbour you trust temporary, clear access to the outage steps and the tank's key details for exactly the days you are gone.