Hurricane prep for reef tanks: the 72-hour outage plan

What actually kills tanks in outages

Hobbyists assume the threat in a hurricane outage is heat. It isn't — at least not first. The order of failure in a powerless reef tank is almost always:

1. Dissolved oxygen drops first. No skimmer, no return pump, no surface agitation. O₂ falls from saturation (~7 mg/L) to under 4 mg/L in 6–12 hours at 78 °F. Fish suffocate.
2. Temperature drifts second. Insulated tanks lose ~1 °F per hour without heat in a 70 °F room. In a closed-up house in August Florida, you're gaining heat: +1 °F per hour toward 88–90 °F.
3. pH crashes third. Without skimmer gas exchange and with rotting biofilms producing CO₂, pH drops to 7.5–7.7 by hour 24.
4. Ammonia rises fourth. By day 3 with dead fish and no biofiltration moving water, ammonia spikes above 0.5 ppm and kills anything still alive.

The good news: every one of these is solved by air movement. A $15 battery-operated air pump moving 2 L/min through an airstone keeps O₂ above 5 mg/L indefinitely. That single intervention buys you 5–7 days. Everything else in this guide is about extending that window or making it more comfortable.

Two weeks out (May 15, or when the season's first depression forms)

This is the once-a-year prep, not the storm-specific one. Do it before the season starts:

• Pre-mix 30–50 gal of saltwater. Store in food-grade Brutes with lids. Tape salinity and mix date to each container. Rotate annually — fresh-mixed saltwater stores 6 months sealed without issue.
• Stock 25 gal RO/DI water. Same Brute, same labelling. Top-off only, no salt.
• Test the generator under load. Run the actual reef-tank equipment off it for 30 minutes. Battery-cranked generators die mid-storm because nobody started them since last hurricane season.
• Charge the deep-cycle battery for the battery-air setup. Top-up monthly via trickle charger; sulfated batteries are useless when you need them.
• Inventory the food: 30 days of frozen Mysis, 30 days of pellets in airtight container. Frozen food survives a 3-day outage in a closed freezer.
• Replace surge protectors on the tank — every cord, including the controller. Surge protectors degrade silently over 18–24 months.
• Update phone numbers: nearest LFS, fish-clubmate within 30 miles, the reefer who has a generator if you don't.

72 hours before landfall

When the cone settles within 100 miles of you and landfall is < 72 hours:

1. Stop feeding heavily. Feed lightly once per day until 24 hours out, then stop. Fish can fast 7 days easily; the lower waste production buys you ammonia headroom.
2. Do a 20–30 % water change with the pre-mixed saltwater. Top off the change tank with the RO/DI you stockpiled.
3. Clean the skimmer cup. When it's running on a generator post-storm, you want it pulling clean — not back-flowing through a clogged neck.
4. Replace any worn equipment: heater on its last legs, return pump making noise. Storm power is when those die.
5. Pull rotten food / dead snails from the tank. Anything organic that's dying needs to be out before the outage.
6. Top off freshwater reservoirs — drinking water for you, RO/DI for the tank.
7. Move frags down. If a chiller fails and the tank warms, deeper corals heat-stress less.
8. Photograph the tank for insurance — close-ups of livestock, full-tank shots, equipment serial numbers visible.

During the outage

The moment you lose power, the priority order is:

1. Air on within 5 minutes. Battery air pump → airstone → tank. If you have multiple tanks, one airstone per 30 gallons.
2. Insulate the tank. Wrap blankets, towels, or pre-cut foam insulation around the tank to slow temperature drift in either direction.
3. Close blinds and curtains. In Florida or the Carolinas in summer, this is the difference between 84 °F and 90 °F inside the house.
4. Generator on the return pump only — not the heater unless ambient drops < 70 °F, not the lights at all. The return pump alone keeps O₂ stable, moves water, and prevents thermal stratification.
5. Skip skimmer until day 2. A skimmer in a no-feed tank for 24 hours is over-skimming; let it wait.
6. Test ammonia daily at minimum. NH₃ above 0.25 ppm warrants a 15 % water change with pre-mixed saltwater.
7. Don't open the freezer. Frozen food survives 48 h in a sealed freezer; opening cuts that to 24 h.

After power comes back

The post-storm period is when more livestock dies than during the outage itself, because reefers turn everything back on at once and crash a tank that was holding stable.

1. Wait 30 minutes before restarting equipment. Grid voltage is unstable for the first half-hour after restoration.
2. Pumps first, lights last. Bring the return pump up, then the skimmer, then circulation, then heater. Lights stay off for 24 hours minimum — a tank that just sat dark for 3 days doesn't want immediate full-blue. Photobleaching risk is real.
3. Test everything: NH₃, NO₂, NO₃, PO₄, alkalinity, pH, salinity, temperature. Salinity may have crept up from evaporation; top off cold and slow.
4. 30 % water change on day 1 regardless of what the tests show. Pre-mixed saltwater, slow drip.
5. Feed lightly for the first 48 hours. The biofilter has been working hard on whatever ammonia accumulated; don't shock it.
6. Photograph livestock for losses if you intend to file an insurance claim. Most homeowner policies require photos within 72 hours of the event.

Battery air supply, sized

The single piece of equipment that saves the most reef tanks is a $15–80 battery air pump. The good ones run on D-cells or built-in lithium; better ones plug into a 12 V deep-cycle battery via cigarette plug and run for 5+ days. Here's the math:

• Air requirement: ~0.5 L/min air per 25 gallons of tank water for emergency aeration. A 75-gal tank wants 1.5 L/min minimum.
• D-cell pumps (Marina Battery Air Pump): 2 L/min, runs 24–36 h on fresh D-cells. Keep 8 D-cells stockpiled.
• 12 V on deep-cycle: a 100 Ah AGM battery + 12 V air pump (Aquatop, AquaForest) runs continuously for 5–7 days. Recharge with a small solar panel or car alternator.
• Powerheads on UPS: a 600 W UPS will run a Maxspect Gyre or small powerhead for ~2 hours. Useful as a bridge while you set up the battery system, not as primary.

Generator sizing for a reef tank

A reef tank's 72-hour generator load is mostly the return pump and intermittent heater. Sized for that, you can run a 90-gal reef on a small inverter generator that's also quiet enough not to draw thieves.

• Minimum viable: 1,000 W inverter generator. Honda EU1000i or equivalent. Runs a 60 W return pump, a 200 W heater on 30 % duty cycle, and a small fan. Fuel: 0.5 gal gas per 8 hours at quarter load.
• Comfortable: 2,000 W inverter. Honda EU2200i, Generac iQ2000, Westinghouse iGen2200. Adds the skimmer, controller, refugium light, and a window AC unit for the room. Fuel: 0.8 gal per 8 hours at quarter load.
• Run the generator outdoors only, 20 ft from any window or vent. CO from generators in garages or near windows kills people every hurricane season — the National Weather Service tracks this annually.
• Surge protector + line-conditioning UPS between the generator and your tank electronics. Inverter generators are clean, but conventional generators aren't — and the difference will fry an Apex.
• Fuel storage: 5–10 gal in metal jerry cans, treated with Sta-bil for 6-month storage. Refresh annually before season.

The supply list

Tank-specific only. (Your home/family supply list is at ready.gov/hurricanes.)

• 50 gal pre-mixed saltwater (matched salinity, sealed Brutes)
• 25 gal RO/DI water (sealed Brutes)
• 1 battery air pump per tank + spare batteries (D-cell or AGM)
• 100 Ah deep-cycle AGM battery + 12 V plug for the pump
• 1,000–2,000 W inverter generator + 5 gal stabilised fuel
• 1 surge protector / UPS between generator and electronics
• Pre-cut foam tank insulation panels (or 3 wool blankets minimum)
• Battery-powered headlamp + 2 spare battery sets
• Ammonia, nitrite, nitrate, pH, salinity test kits — all in date
• 30-day reserve of fish food (frozen + pellet)
• Coral dip + clean QT bucket in case you need to triage corals
• Phone numbers: nearest LFS, two reefer friends, insurance agent

Regional notes

The threat profile differs by where you keep reef:

• Florida — Gulf and Atlantic coasts: Repeated direct-hit risk every season. Generator + battery air are mandatory, not optional. Mid-July through October is highest risk. Expect 3–7 day outages from a Cat 3+ direct hit; up to 14 days inland after major systems.
• Carolinas: Hurricanes weaken by landfall but power outages last longer because grids are more spread out. Plan for 5–10 day outages in the worst case. Pine-tree damage to lines is the most common cause.
• Gulf coast (TX, LA, MS, AL): Storm surge is the differentiator. If you're in an evacuation zone, plan to leave and accept tank loss as possible. Don't shelter in place with a reef tank in a storm-surge zone — humans first.
• Northeast (NJ, NY, RI, MA): Tropical storms more than hurricanes, but Sandy taught reefers that 7-day outages are real here too. Same kit list, lower probability.
• Inland from the coast: Power outages from downed trees during tropical storm-force winds happen 100+ miles inland. The Carolinas saw 5-day outages from Hurricane Helene as far as Asheville (300+ miles inland). Don't assume distance = safety.

Bottom line

Reef tanks die in hurricanes from oxygen, not heat. A $15 battery pump and an extra hour of prep are the difference between starting over and losing a few snails. Build the kit in May, test the generator in June, and never check the cone after midnight without your equipment already deployed.

Last reviewed for the 2026 Atlantic hurricane season. NOAA pre-season outlooks publish in late May; check the National Hurricane Center for current season forecasts.