How the running cost is calculated
Every piece of equipment has a power rating in watts. Electricity is sold by the kilowatt-hour (kWh): one kWh is 1,000 watts running for one hour.
The filter runs all day and all night, so a 10 W filter uses 10 × 24 ÷ 1,000 = 0.24 kWh a day.
The light runs only when you switch it on. A 20 W LED on for 8 hours uses 0.16 kWh a day.
The heater is the tricky one, because it switches itself on and off. A 150 W heater does not use 150 W all day. It only replaces the heat the tank loses to the room. A heater of the right size is on for roughly 40% of the time in the room it was sized for, so the calculator takes the wattage from our heater size calculator and counts 40% of it. In a warm room the heater hardly runs; in a cold room it runs most of the time.
Worked example. A 29 gallon tank at 78 °F in a 68 °F room needs a heater of about 145 W. On average it draws 145 × 0.4 = 58 W, which is 1.4 kWh a day. A typical filter (9 W) adds 0.2 kWh and a typical LED (16 W for 8 hours) adds 0.13 kWh. That is about 1.7 kWh a day, or 52 kWh a month. At 17 cents per kWh, the tank costs about $9 a month.
What costs the most
In most homes the heater is two thirds or more of the bill. The filter and an LED light cost very little. So the best ways to save money are all about heat:
- Use a lid. Evaporation carries away a lot of heat.
- Keep the tank in a warm room, away from drafty windows and outside doors.
- Insulate the back and sides with foam board or a background.
- Do not overheat. Most tropical fish are happy at 76–78 °F (24–26 °C). Each extra degree costs money.
- Choose fish that suit your room. White Cloud minnows, zebra danios and fancy goldfish need no heater in a normal home.
Typical figures we use
If you do not know your equipment's wattage, the calculator uses typical figures: a filter of about 0.08 W per liter of tank (never less than 3 W), and an LED light of about 0.15 W per liter. Old fluorescent tubes and high-powered plant or reef lights use much more. If you have those, open "I know my equipment's wattage" and type the real figures from the labels.
Common mistakes
- Multiplying the heater's full wattage by 24 hours. A heater cycles on and off, so that gives a bill two or three times too high.
- Forgetting the light is the one thing you control. A timer set to 6–8 hours saves money and slows algae.
- Using an old price. Electricity prices change: take the price per kWh from your latest bill.
- Turning the filter off at night to save money. It costs pennies to run, and the bacteria in it start to die within hours without flow.
Questions and answers
How much does it cost to run a fish tank per month?
A typical heated 29 gallon tropical tank uses about 50 kWh a month: roughly $9 at 17 cents per kWh. A small unheated tank costs under $2 a month. A heated 75 gallon tank often costs $15–25.
Do fish tanks use a lot of electricity?
Less than most people fear. A medium tropical tank uses about as much as a modern fridge. The heater is most of it, so tanks in warm rooms cost much less.
How much electricity does an aquarium heater use?
A heater only runs when the water cools, about 40% of the time in a normal room. A 100 W heater therefore uses about 1 kWh a day, not 2.4.
How much does a 10 gallon tank cost to run?
About 15–20 kWh a month with a heater in a normal room: around $3 at 17 cents per kWh.
Should I turn the aquarium heater off at night?
No. Fish need a steady temperature, and reheating the tank each morning saves nothing. Leave the heater plugged in and let its thermostat do the work.
Numbers for standard tanks
Have a standard tank? Its size, weight, heater and stocking are already worked out.
- 10 gallon tank
- 20 gallon long tank
- 29 gallon tank
- 40 gallon breeder tank
- 55 gallon tank
- 75 gallon tank
- 125 gallon tank
- All tank sizes
Sources
- Power × time: 1 kWh = 1,000 W for one hour (SI definition)
- Aqueon heater guidance: 5 W per gallon up to 55 gal, 3 W per gallon over 60 gal, as quoted by Build Your Aquarium