Power outages are more than an inconvenience for reef tanks. Oxygen drops fast, and temperature swings can be deadly. A simple plan can buy you hours or days.
What fails first during an outage
In most reef tanks, oxygen is the first emergency. Surface agitation stops when return pumps and powerheads shut off. Fish start breathing hard within 30 to 90 minutes in crowded tanks.
Temperature is the next threat. A reef tank is safest near 77–79°F. Try to keep swings under 2°F in 24 hours. In winter, a 10°F room can chill a 75-gallon tank several degrees overnight.
Filtration can pause longer than many think. Bacteria live on rock and sand. Still, a sealed sump can go anoxic. If power is out over 6 hours, avoid restarting a stagnant sump without checking smell.
Light is usually last on the priority list. Corals can handle a day or two of low light. Focus on air, flow, and heat first. Review your oxygenation basics before you buy gear.
- First goal: keep water moving at the surface.
- Second goal: hold 76–80°F as steadily as possible.
- Third goal: prevent toxic water in sumps and reactors.
Choose the right backup power setup
Start with a load list. Many reef keepers overbuy watts and underbuy runtime. Write down each device and its watts. A typical plan powers one circulation pump at 10–30W and one heater at 100–300W.
Battery air pumps are the cheapest insurance. Use two units and two airstones. Aim for at least 2–4 LPM total air on a 75-gallon tank. Place stones near the surface to maximize gas exchange.
For longer outages, use a UPS or a lithium power station. A UPS works best for low-draw pumps. A 1000VA UPS may only run a 20W pump for 6–12 hours. A 500Wh power station can run that same pump about 20 hours.
Generators solve multi-day events. A 2000W inverter generator is quiet and fuel efficient. Run it outside only, with a long cord. Power your heater in short cycles to save fuel. See our equipment priority list to plan loads.
- Pick one DC circulation pump with a battery option if possible.
- Keep a spare heater and a simple thermometer in the cabinet.
- Store fresh fuel and test-run the generator monthly.
Step-by-step outage plan and common mistakes
When power drops, act in the first 10 minutes. Feed nothing. Open the canopy for gas exchange. Start battery air pumps right away. If you have a power station, run one powerhead aimed at the surface.
Manage temperature with insulation first. Wrap the tank with blankets, but keep vents open for air lines. In summer, float frozen water bottles in a bag. Change them every 2–3 hours as needed. Avoid rapid cooling.
Be careful with sumps and skimmers. A skimmer can overflow after restart. Unplug it until water levels stabilize. If the sump smells like sulfur, do not pump that water into the display. Remove and discard the stagnant water first.
After power returns, ramp up slowly. Restore flow first, then heat, then filtration. Test ammonia within 6–12 hours. Keep Prime or another detoxifier on hand. Review ammonia spike troubleshooting if fish gasp or corals slime.
- Mistake: running a heater on a small UPS and draining it fast.
- Mistake: feeding to “reduce stress” during low oxygen.
- Mistake: restarting a stagnant sump without checking odor.
Emergency power is easiest when you plan for your tank size and climate. Cover oxygen first, then temperature, then filtration. Test your gear now, and you will sleep better during storms.
Sources: NOAA National Weather Service outage safety guidance; Reef aquaria husbandry references on dissolved oxygen and temperature stability; Manufacturer runtime calculators for UPS and portable power stations.
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