What's the most expensive part of running a reef tank?

Almost always the heater. A 200–300 W heater at 30 % duty cycle runs $7–11 per month at US average rates. The return pump is a steady $4–8/mo at 50–100 W continuous. Lights are usually third at $2–4/mo for a typical 90 W reef LED on an 8-hour schedule.

Does an LED save much vs metal halide?

Yes. A 250 W metal halide on an 8-hour schedule costs ~$10/mo. A 90 W LED on the same schedule costs ~$3.50/mo — and you replace bulbs every 12 months on halides ($30–60 each) but maintain LEDs for 5+ years. Three-year operating cost favours LED by ~$400+.

Should I run a chiller or a fan?

A surface fan over the sump is 5–10 W vs a chiller's 200–600 W. If a fan + open lid drops your tank temp 3–4 °F, that's usually enough — and the evaporation cooling is essentially free compared to a chiller's annual cost ($200–500/yr in hot climates).

Aquarium Electric Bill Calculator — monthly cost by device

JavaScript is disabled in your browser, so the interactive calculator below won't run. The math, formula, and worked example are all written out further down this page under “How this is calculated.” Enable JS (or open this page in another browser) to use the live calculator.

Whether you compute by hand or in the calculator, the same caveat applies: verify against your test kit and the linked primary source before dosing. reefcalcs is reference information, not veterinary or engineering advice.

Electric bill

USD/kWh

Device

Watts

Duty cycle

Hours/day

Monthly cost

$25.69

Monthly kWh

160.6kWh

Annual cost

$308

Device	kWh/mo	$/mo
Return pump	36.5	$5.84
Powerheads	21.9	$3.50
Skimmer	14.6	$2.34
Heater	65.7	$10.51
Lights	21.9	$3.50

US average residential rate is ~$0.16/kWh (EIA 2025). Look up your actual rate on your utility bill for accurate numbers.

Gear for thisAffiliate links

EcoTech Marine Vectra M2 return pump ~$350 · View on Amazon →

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How this is calculated

Per-device monthly kWh = watts × duty × 24 hr × 30.42 days / 1000

Duty cycles:
  Always-on (skimmer, return, powerhead): 1.00
  Heater (cycles to maintain temp):       0.30
  Lights-only:                            hours/day ÷ 24
  Custom 50% duty:                        0.50
  Custom 25% duty:                        0.25

Monthly cost = monthly_kWh × rate_per_kWh
Annual cost  = monthly_cost × 12

Heater duty cycle of 30 % is the average for indoor temperate climates with a 4–6 °F gap between tank and room temperature. In a colder room (basement, garage), bump to 40–50 %; in a warm room or sunny window, drop to 15–20 %.

The biggest savings target is usually the heater. A 200 W heater in a well-insulated cabinet runs ~30 % duty; the same heater on an open-top tank in a drafty room runs ~50 %. Lid + insulation can drop the heater cost by 30–40 %.

FAQ

What's the most expensive part of running a reef tank?: Almost always the heater. A 200–300 W heater at 30 % duty cycle runs $7–11 per month at US average rates. The return pump is a steady $4–8/mo at 50–100 W continuous. Lights are usually third at $2–4/mo for a typical 90 W reef LED on an 8-hour schedule.
Does an LED save much vs metal halide?: Yes. A 250 W metal halide on an 8-hour schedule costs ~$10/mo. A 90 W LED on the same schedule costs ~$3.50/mo — and you replace bulbs every 12 months on halides ($30–60 each) but maintain LEDs for 5+ years. Three-year operating cost favours LED by ~$400+.
Should I run a chiller or a fan?: A surface fan over the sump is 5–10 W vs a chiller's 200–600 W. If a fan + open lid drops your tank temp 3–4 °F, that's usually enough — and the evaporation cooling is essentially free compared to a chiller's annual cost ($200–500/yr in hot climates).

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Sources & references

1.
EIA — average US residential electricity rate
https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a
2.
BRS — aquarium electricity calculator
https://www.bulkreefsupply.com/reef-calculator/electric-bill-calculator

Last reviewed 2026-09-30