How much electricity does a fish tank use per month in the UK?
A 200 litre tropical aquarium with a 200 watt heater, an external filter and an LED light uses roughly 1.44 kilowatt hours a day, which is 37.6p at the Ofgem cap rate of 26.11p per kWh and £11.43 over a month. A 60 litre starter tank runs on about 0.62 kilowatt hours a day, or £4.96 a month.
Three things draw the power, not one
An aquarium is a heater, a pump and a light sharing a plug board, and the only one that costs real money is the heater.
Fluval rates its M series heaters at 100 watts for tanks up to 100 litres, 150 watts to 150 litres and 200 watts to 200 litres, with the E series stepping up to 300 watts for tanks near 375 litres. A heater only draws that power while the thermostat calls for heat. In a living room held around 20 degrees, with a tank at 25, we assume it runs about a fifth to a quarter of each hour, which is our own working assumption rather than a published figure. On a 200 watt heater that averages roughly 44 watts.
The filter runs every second of every day and hardly registers. EHEIM publishes 8 watts for the classic 250, which moves 440 litres an hour and suits tanks from 80 to 250 litres. The light is a fixed cost for the hours it is on. Fluval rates the Aquasky 3.0 at 18 watts for a 61 to 93 centimetre tank and 27 watts for a 91 to 122 centimetre one, and eight hours a day of the larger unit averages out at 9 watts across the full day.
Add those together for a 200 litre tropical tank and you get about 60 watts of continuous average draw.
Work it out for your own fish tank
Type in the wattage from the plate on the back, then your own unit rate. The numbers update as you type.
What that costs, by tank size
| Tank | Average draw | Per day | Per month | Per year |
|---|---|---|---|---|
| 25 litre nano, 50W heater | 11 W | 6.9p | £2.10 | £25.16 |
| 60 litre starter, 100W heater | 26 W | 16.3p | £4.96 | £59.47 |
| 200 litre tropical, 200W heater | 60 W | 37.6p | £11.43 | £137.20 |
| 200 litre in a cold room | 96 W | 60.2p | £18.29 | £219.58 |
| 300 litre marine with pumps | 200 W | £1.25 | £38.10 | £457.40 |
The fourth row is the one that surprises people. Nothing about the tank has changed, only the room around it. A conservatory or an unheated spare bedroom in January forces the heater to run closer to 40 per cent of the time instead of 20, and the monthly bill rises by £7 without a single new piece of equipment.
| Appliance | Typical draw | Usage we assume | Per hour (UK) | Per usage (UK) | Per month (UK) | Per hour (US) |
|---|---|---|---|---|---|---|
| Fish tank | 60 W | per 24 hours, heater and pump | 1.6p | 37.6p | £11.40 | 1.1 cents |
Rates: Ofgem cap 1 July to 30 September 2026 at 26.11p per kWh (source), EIA residential average June 2026 at 18.34 cents per kWh (source). Checked 2026-09-22.
Doing the sum for your own tank
Work out the average, not the peak. Take the heater wattage and multiply it by the fraction of the hour you think it runs, add the filter wattage in full, then add the light wattage multiplied by its hours divided by 24.
For a 200 litre tank that is 200 multiplied by 0.22, which is 44 watts, plus 8 watts for the filter, plus 27 multiplied by 8 divided by 24, which is 9 watts. The total is 61 watts. Multiply by 24 hours and divide by a thousand to get 1.46 kilowatt hours a day, then multiply by 26.11p for 38p.
If you want the honest version rather than the estimate, a plug in energy monitor under £15 will read the whole plug board for a week and settle the argument for good.
Five ways to cut an aquarium bill
- Move the tank away from an external wall or a draughty window. The heater is fighting the room, so the room is where the saving is.
- Fit a lid or a cover glass if the tank does not have one. Evaporation carries away heat faster than conduction through the glass, and a lid also stops the water level dropping every few days.
- Put the light on a timer set to eight hours. Longer photoperiods cost money and grow algae, which costs you a water change on top.
- Insulate the back and the sides with a sheet of polystyrene behind the tank, which is invisible once the background is on and cuts heat loss through the largest cold surface.
- Choose the right size heater rather than the biggest one. An oversized heater does not use more energy in principle, but it overshoots the set point and cycles harder, and in a power cut it is also the one most likely to cook the tank when the thermostat sticks.
What an aquarium costs in the United States
At the EIA residential average of 18.34 cents per kilowatt hour, the same 200 litre tropical tank costs 26 cents a day and $8.03 a month. A 55 gallon tank in a Texas home, where electricity averages under 16 cents, comes in around $7 a month, while the identical tank in California at nearly 35 cents costs $15.30. Marine keepers with return pumps, wave makers and metal halide lighting should expect to multiply those numbers by three or four.
Is it worth turning things off
The heater and the filter are not luxuries, so the only honest saving is on the light and on the room. Switching the filter off overnight saves about 2p a week and risks the biological filter, which is the sort of trade nobody should take. The light on a sensible timer saves real money and improves the tank. Everything else comes down to where the tank sits and whether the lid is on.
Common questions
Does a fish tank heater use a lot of electricity?
The heater is the biggest item on the list, though not for the reason most people assume. A 200 watt heater does not draw 200 watts all day, it draws 200 watts for the fraction of each hour needed to replace lost heat, which in a normally heated room is around a fifth of the time. That still leaves it responsible for roughly three quarters of the tank's monthly total.
Does a fish tank filter use a lot of electricity?
No. An EHEIM classic 250 external filter draws 8 watts and runs continuously, which is 0.19 kilowatt hours a day and about £1.52 a month. Turning it off overnight to save money is a false economy, because the bacteria in the media start dying within a couple of hours.
Does a 10 gallon fish tank use a lot of electricity?
A 45 litre tank with a 50 watt heater, a small internal filter and an LED strip uses around 0.26 kilowatt hours a day, which is 6.9p and about £2.10 a month. That is less than leaving a broadband router on, and the router costs more.
How much does it cost to run a fish tank per day in the UK?
Between 7p for a nano tank and around £1.25 for a heavily stocked marine setup, with a typical 200 litre tropical tank at 37.6p a day. The spread comes from the heater, the room temperature and whether there are pumps running around the clock.