Small Fish, Crowded Tank, Fast Drift
A guppy tank looks like the easiest aquarium to protect in a power cut, and in a well-stocked breeding setup it can be one of the quickest to drift. Guppies are tropical, so warmth matters, and they are usually kept in numbers, with fry hiding in the plants and females carrying the next batch, so waste keeps being produced in a modest volume of water even after the filter stops. The fish themselves are hardy and forgiving of a slow temperature slide, which gives you time, but that hardiness tempts owners to keep checking, feeding and fussing, and each of those habits makes the still water worse rather than better.
Wrap the Tank and Keep It Closed
Insulate the aquarium with towels or a blanket around the glass and over the lid, and keep the lid shut between brief checks so the warm surface air the adults and fry rely on stays in place. Dim the room or cover the front glass, because a resting school in the plants wastes less energy and produces less waste than one startled by torches every few minutes. If the room is cold and the thermometer is clearly falling, float a sealed container of warm water inside and watch it closely, never pouring hot water straight in among fish small enough to be scalded by a careless stream. Keep children and pets away from the open cabinet where torches, batteries and stored chemicals suddenly come out.
Gentle Air and No Food Until Flow Returns
Run a battery air pump gently if you have one, ideally through a sponge that keeps some filter bacteria working while it lifts oxygen through the water column, and set the flow kindly; a violent bubble wall in a small tank exhausts fry. Without a pump, disturb the surface with a clean jug of tank water poured from a small height at intervals. Feed nothing during the outage, for adults or fry. A guppy colony misses food safely for far longer than it tolerates the ammonia that uneaten flakes and decaying fry food release into unfiltered water, and the plants will offer the fry more grazing than you expect.
Restart, Count and Test Afterwards
When the power returns, make sure the heater is actually heating and the filter is primed and flowing before you feed a small meal and watch it disappear. Test for ammonia over the next few days, because a long outage thins the filter colony just as a hungry colony starts eating again, and change modest amounts of conditioned water at the tank's own temperature whenever readings climb. Count adults if you can without a chase, check the plant thickets for fry, and expect a quiet day or two from females that were close to giving birth; stress delays deliveries, and a calm, warm, clean tank is what brings the colony back to normal.
Plan for the Outage That Starts Without You
The dangerous cut is the one that begins while the house is empty, so keep the towels, pump and spare batteries beside the tank with a short note saying what to do first, and agree with someone nearby that they can come in and wrap the aquarium. If, after heat, flow and clean readings are restored, several guppies keep gasping at the surface, clamp their fins or die over the following days, contact an aquatic veterinarian and share the outage length and lowest temperature you recorded. Arranging that nearby help through KinsLe's Circle of Love connects your guppy tank with local pet lovers ahead of time, so an empty house in a power cut does not mean an unattended tank.