Step-by-step response
First 30 minutes: Assess + start oxygenPlug in battery-powered air pump (Marina, Penn-Plax) - immediately starts oxygenation. Without power-out air supply, fish suffocate within 4-12 hours depending on bioload.
Manage temperature: First hourWinter: insulate tank with blankets (NOT directly on tank, drape over surrounding sides). Summer: drape damp towels over tank for evaporative cooling. Keep room cool with windows open OR closed depending on outside temp.
Hour 1-12: Manual circulationEvery 1-2 hours: stir water with a clean cup or pour water from a height of 6 inches above surface. This re-oxygenates manually if no battery air pump.
Hour 12-24: Test waterCheck ammonia. Bio-filter starves of oxygen and dies off after 12+ hours - ammonia rises rapidly. Have Prime ready to detoxify.
Hour 24+: Conserve fishStop feeding entirely. Bio-filter is compromised so any food = ammonia spike. Test ammonia every 6 hours. Dose Prime as needed.
Power restored: Slow recoveryDon't feed for 24 hours after power returns. Test ammonia + nitrite hourly for first 6 hours. Bio-filter takes 3-7 days to fully recover.
FAQ
How long can fish survive without a filter?
Marine fish: 12-24 hours with adequate oxygenation. Freshwater: 24-48 hours. The killer is oxygen depletion + ammonia accumulation, not lack of "filtration" specifically.
Do I need a generator for my aquarium?
For tanks under 75g: a $25 battery air pump is enough for 24-48 hour outages. For tanks 125g+ with heavy stocking + reef: consider a UPS or generator if your area has frequent outages.
What's the most important equipment in a power outage?
#1: Air pump for oxygen. #2: Heater (winter). #3: Return pump for circulation. Lights are LAST priority - fish survive darkness fine for days.