Most fish tanks don’t use a lot of electricity. A typical freshwater aquarium costs roughly $1.50 per month for every 10 gallons when you factor in the filter, lights, and heater. That puts a standard 55-gallon heated tank somewhere around $8 to $10 a month, or about $100 to $120 a year. That’s comparable to running a couple of extra light bulbs around the house. Saltwater reef tanks, however, can cost two to four times more due to extra equipment.
What Actually Uses Power in a Fish Tank
Three pieces of equipment account for nearly all aquarium electricity use: the heater, the filter, and the lights. Of these, the heater is almost always the biggest draw, but only if you’re keeping tropical fish that need water warmer than your room temperature.
Filters run 24/7 but pull surprisingly little power. A small hang-on-back filter uses 3 to 12 watts. A medium canister filter draws 15 to 35 watts. Even a large canister filter, the kind you’d use on a 75-gallon tank, typically maxes out around 25 to 60 watts. At 30 watts running constantly, a canister filter adds roughly $3 per month to your electric bill at current U.S. electricity rates (about 13.6 cents per kilowatt-hour).
Lights are on a timer, usually 8 to 10 hours a day, so their contribution is modest in most freshwater setups. Basic LED fixtures for freshwater tanks draw very little. Reef tank lighting for coral growth is a different story, pulling significantly more wattage for longer periods.
The Heater Is the Biggest Variable
Your heater’s electricity use depends almost entirely on one thing: how much warmer the tank needs to be compared to the room it’s in. If your room stays at 70°F and your fish need 78°F, that 8-degree gap is what the heater has to maintain constantly. The bigger the gap, the more the heater cycles on, and the more electricity it uses.
A useful rule of thumb: about 1.5 watts per gallon will raise and hold the water temperature 10°F above room temperature. For a 55-gallon tank, that translates to roughly 80 watts of continuous equivalent draw. Over a month (about 720 hours), that’s around 58 kilowatt-hours just for heating, costing about $8.
If your room is already warm, say 76°F, and you only need to raise the water a couple of degrees, your heater barely runs at all. In that case, the cost drops dramatically. Unheated tanks (like those keeping goldfish or white cloud minnows at room temperature) cost roughly $0.30 per month per 10 gallons, since you’re only powering the filter and lights.
Smaller tanks actually use more watts per gallon than larger ones because they have more surface area relative to their volume, which means they lose heat faster. A 10-gallon tank needs about 3.5 watts per gallon to hold temperature, while a 100-gallon tank needs only about 2 watts per gallon.
Monthly Cost by Tank Size
These estimates assume a heated freshwater tank keeping water about 8 to 10°F above a 70°F room, using the current U.S. average electricity rate of roughly 13.6 cents per kilowatt-hour:
- 10-gallon tank: $1.50 to $2 per month
- 20-gallon tank: $3 to $4 per month
- 55-gallon tank: $8 to $10 per month
- 75-gallon tank: $10 to $13 per month
- 100-gallon tank: $13 to $17 per month
These numbers include the filter, lights, and heater combined. Your actual cost could be lower if your home runs warm, or higher if you keep your house cool in winter or live in a state with above-average electricity prices. Rates in Hawaii, for instance, are roughly triple the national average.
Saltwater and Reef Tanks Cost More
Saltwater aquariums, particularly reef tanks with live coral, require additional equipment that pushes electricity costs significantly higher. Protein skimmers, wavemaker pumps, high-intensity lighting for coral growth, and sometimes chillers all add to the power draw.
Estimated annual electricity for a freshwater tank runs $120 to $180. A comparable saltwater reef tank typically lands between $240 and $480 per year. That’s roughly $20 to $40 per month, depending on the size and complexity of the setup. The specialized lighting alone can draw more power than an entire freshwater system’s equipment combined.
How to Lower Your Tank’s Energy Use
The single most effective thing you can do is reduce the temperature gap between the room and the tank. Dropping your target temperature from 78°F to 72°F (if your fish species tolerate it) can cut heating costs by two-thirds. For the example of three 50-gallon tanks, one analysis showed monthly costs dropping from $22.50 to $7.50 just by lowering the target temperature.
Keeping the tank in a warmer room helps too. A tank in a basement that stays at 62°F will cost noticeably more to heat than one in a living room at 72°F. Insulating the back and sides of the tank with foam board is a low-tech trick that reduces heat loss through the glass.
Upgrading to DC-powered pumps and return heads can also trim ongoing costs. DC pumps are more energy-efficient than traditional AC models, offer precise flow control, and generally run quieter. The upfront cost is higher, but they pay for themselves over time on tanks that run equipment 24/7. Switching to LED lighting, if you haven’t already, is another easy win since LEDs use a fraction of the power that older fluorescent or metal halide fixtures require.
Putting It in Perspective
A 55-gallon freshwater aquarium uses roughly 100 to 130 kilowatt-hours per year when heated, which is less than a single incandescent light bulb left on for 8 hours a day. A typical U.S. household consumes about 10,500 kilowatt-hours annually, so even a large heated tank represents around 1 to 2 percent of total home electricity use. For most fishkeepers, the cost of electricity is one of the smaller ongoing expenses compared to food, water treatments, and replacement equipment.