How Long Will a Power Station Run Your Reef Tank? (We Did the Watt Math)

It’s 2am. The lights just cut. You’ve got $5K in live coral, two days’ worth of fish food in the system, and 10 minutes before the wrong temperature swing kills everything. Most battery-backup articles tell you to “get a big power station” and move on. We’re going to do the math that actually matters.

The Formula Every Reefer Should Memorize

Stop guessing. The runtime calculation is dead simple:

(Wh × 0.85) ÷ load (watts) = hours

The 0.85 is efficiency loss. You don’t get every watt-hour the battery claims.

BRSTV’s lab testing has been running this formula for years, and it works. Let’s walk two real scenarios:

Scenario 1: 600Wh battery, 15W return pump on low. (600 × 0.85) ÷ 15 = 34 hours. Your coral doesn’t die.

Scenario 2: 1,152Wh battery (EcoFlow Delta 2 territory), full-system draw at 200W. (1,152 × 0.85) ÷ 200 = 4.9 hours. Enough time for power to return on a typical grid event.

That formula is your north star. Everything else is load auditing.

Load Tier Table: What Actually Stays On?

Here’s what BRSTV’s lab testing and Melev’s Reef power audits show:

Tier	Equipment	Typical Watts	EcoFlow Delta 2 (1,024Wh) Runtime
Tier 1 (Flow Only)	Powerheads (battery backup mode) + return pump (low)	~25W	~34 hours
Tier 2 (Flow + Heat)	Powerheads + return pump + heater hold	~325W	~2.7 hours
Tier 3 (Full System)	Everything: flow + heat + skimmer + return (full) + ATO	~500W	~1.7 hours

A return pump like the Abyzz pulls 160–165W at full throttle. Your MP60 powerhead swings from 8W (battery-safe mode) to 43W (full blast). The heater is the load killer—most reef heaters are 150–300W on their own.

The brutal reality: you can’t run your whole reef on a single EcoFlow Delta 2 (1,024Wh) for long. You can keep your coral alive on Tier 1 for days.

Why UPS Mode Wrecks Your Runtime

This is where most people get blindsided. There’s a difference between a UPS (uninterruptible power supply) and a battery hooked straight to DC loads.

BRSTV’s testing measured the same battery powering an EcoTech VorTech MP10 two ways:

• UPS mode (battery → inverter → AC → pump): 5.25–5.75 hours
• DC-native direct draw: 81.5 hours

The inverter—AC conversion—bleeds efficiency. Every inversion costs you 10–15% of your watt-hours as heat. If you’re serious about long-term backup, you want DC-direct circuits to your pump, not inverter-converted AC.

Most affordable power stations (the EcoFlow Delta 2 included) default to AC inverter output. Accept that loss in your math. Plan around it.

Priority Order When the Power Drops

Don’t panic-run everything. Triage.

Bulk Reef Supply’s outage prep guide nails the priority:

1. Flow first. Stagnation kills coral faster than anything else. Keep those powerheads on battery mode—low wattage, maximum runtime.
2. Heat second. Temperature swings wreck tanks, but slow. You have hours before a 5-degree drop matters.
3. Filtration last. Your skimmer and biological filter can sit idle for a few hours. They’ll catch up when power returns.

This isn’t strategy—it’s triage. Coral needs oxygen and current. Everything else is secondary.

What Power Station Actually Fits This Job

You need realistic watt-hours. The EcoFlow Delta 2 (1,024Wh) buys you Tier 1 all day and Tier 2 for a few hours. If you’re running a 500W reef (heater + full flow), you’re looking at 1.7 hours. That’s not backup. That’s a placeholder.

For a serious reef, 2,000+ Wh is the ballpark. The Delta 2 spec sheet shows 1,024Wh capacity, 1,800W AC output, and EPS switchover mode. That near-instant transfer speed matters—your fish won’t even notice the handoff.

But don’t buy specs. Buy watt-hours matched to your load tier. Do the math first.

Math Is the Move

This isn’t complicated. Add up your gear, multiply by 0.85, divide into your battery capacity, and you have your answer. No guessing. No marketing copy. Just the physics of power.

You’ve probably solved the same Wh ÷ load math we ran on a fridge. The principle doesn’t change whether you’re keeping frozen food or live coral alive. Same logic applies to the sump-pump outage scenario—you’re buying time until the grid comes back.

For overnight outages, cold-weather LFP vs NMC discharge curves matter less than capacity does. Your reef tank lives in climate control. You’re not fighting temperature loss on the battery itself.

The reefs that survive power events are the ones where someone did the math at a calm moment, not at 2am in a panic. Do it now.