A fish tank's monthly running cost depends on heater size and duty cycle, filter wattage, lighting schedule, air pumps, local electricity price and recurring supplies. The heater is often the largest variable in a tropical tank because it cycles according to room temperature rather than running continuously. Use actual device wattages and your own tariff instead of relying on a universal monthly figure.
Two identical tanks can have very different running costs in different homes. A warm room, efficient lid and modest lighting can reduce energy use, while a cold room or powerful planted-tank light can push it up.
Electricity is the easiest part to calculate
For each device, multiply watts by hours used, divide by 1,000 to get kilowatt-hours, then multiply by your electricity price. For heaters, estimate duty cycle rather than assuming the rated wattage runs 24 hours a day.
Our electricity calculator lets you enter equipment and tariff assumptions directly.
Recurring non-electric costs
- Fish food.
- Water conditioner.
- Test-kit reagents or strips.
- Plant fertiliser where used.
- Replacement lamps or equipment over the long term.
- Tap water charges where relevant.
What usually costs most
In heated freshwater aquariums, the heater often dominates variable electricity use. Filter pumps run constantly but are usually lower wattage. Lighting can become significant in large planted tanks with long photoperiods.
Measure rather than guess if you want a precise household figure.
Do not cut costs by compromising welfare
Turning off filtration at night or allowing tropical tanks to swing outside species-appropriate temperature ranges is not sensible energy saving. Focus on efficient equipment, lids, room temperature and sensible lighting schedules instead.
Reliability still matters more than shaving a few pence from essential life-support equipment.
Frequently asked questions
Does a fish tank use a lot of electricity?
It depends on size, heating demand and lighting. Small efficient tanks can use relatively little; large heated planted tanks use more.
Can I turn the filter off at night to save money?
No. Aquarium filters should normally run continuously to maintain circulation and biological filtration.
How can I get an accurate monthly figure?
Use the wattage and run time of each device with your actual electricity tariff, ideally checked with a plug-in energy meter.
Sources and further reading
This guide separates general aquarium arithmetic from fish-welfare decisions. For species-specific limits, always check the needs of the fish you intend to keep.