Ask what ends a guppy's power cut badly and the answer is cold, arriving quietly. Guppies are small tropical fish with almost no body mass to hold heat, living in tanks that are heated precisely because room temperature is below their comfort. Filtration and light matter far less over a day than the slow slide of the thermometer, so a guppy outage plan is insulation, observation, and calm.
Wrap the guppy tank before the water notices
Insulate early, while the guppy tank still holds its heated warmth: blankets, towels, or a duvet around the glass and over the top slow the loss to a drift these fish can follow rather than a drop that shocks them. A larger tank buys hours; a small one cools fast, which is why small guppy tanks get wrapped first in a multi-tank home. Never add warm water directly, and never tape heat sources against the glass — a small volume overshoots in minutes, and a swing upward after a slide downward is harder on a guppy than the slide itself. If the household has any safe room heating, the guppies benefit most from simply being in that room.
Calm water, cover, and no chasing
Keep the guppy group in its own tank, in the dark, undisturbed. Plants — real or artificial — should stay exactly where they are, because the group shelters among them and any fry in the tank hide there from adults; a power cut is a common moment for a pregnant female to drop fry early, and cover decides how many survive it. Do not net fish to count them, do not move males and females apart, and do not clean the glass for a better look. Every disturbance burns energy a chilled guppy needs. A battery airstone, if used, runs gently: a strong current in a small tank exhausts weak swimmers.
Feeding stops; the filter waits wet
Guppies foul water slowly, and a stopped filter still matters less than warmth, so the feeding rule is simple: nothing for the duration, or a single tiny pinch on a cut stretching into another day. Uneaten fine food in still water clouds it quickly relative to a small tank's volume. Keep filter media submerged in tank water if the filter dries or is opened, so its bacteria are alive when power returns. When the heater restarts, let it bring the tank back at its own pace and confirm the thermometer agrees with the heater's setting before assuming the reading.
The signs that cold is winning
Guppies that hang motionless near the surface or bottom, lose their colour, shimmy in place, or stop responding to movement outside the glass are cold-stressed rather than merely resting, and clamped fins alongside that picture strengthen it. Warming the room, adding another layer of insulation, and patience are the responses — not warm water. Pale, listless fish that do not recover as the temperature returns, or any fish showing spots or fraying in the days after, deserve advice from a vet or aquatic specialist, since stress and illness often arrive together. During the cut, KinsLe Kinny can help you judge a guppy group's temperature readings hour by hour, kept beside their profile.