How much does an aquarium cost to run per month?
Somewhere between the price of a coffee and the price of a fridge, and the spread is almost entirely the heater and the lights. The table runs seven ordinary setups through the same engine as the tool — the heater line is the tank's actual heat loss at a 72 °F room, not a wattage — at the US average 18 ¢ per kWh. A 10 gal community with a lid costs about $2.80 a month; a 75 gal high-light planted about $14; an open-top 120 gal mixed reef $41, with the heater and the pumps between them beating the lights.
| Setup | kWh / day | Heater | Lights | Pumps | Per month | Per year |
|---|---|---|---|---|---|---|
| 10 gal community, lid | 0.5 | 61 % | 16 % | 23 % | $2.80 | $34 |
| 29 gal community, lid | 1 | 66 % | 14 % | 19 % | $5.45 | $65 |
| 55 gal community, lid, canister | 1.7 | 64 % | 14 % | 21 % | $9.18 | $110 |
| 75 gal high-light planted, lid | 2.5 | 44 % | 29 % | 24 % | $14 | $163 |
| 125 gal community, lid, two canisters | 3.1 | 46 % | 23 % | 31 % | $17 | $204 |
| 40 gal breeder reef, open top | 3.9 | 30 % | 21 % | 47 % | $21 | $254 |
| 120 gal mixed reef, open top | 7.6 | 21 % | 26 % | 49 % | $41 | $498 |
78 °F water, 72 °F average room, 50 % RH, 18 ¢/kWh. Equipment watts are typical of what is sold (lights 10 / 18 / 30 / 90 / 90 / 100 / 250 W on 8 h; pumps 24 h, with their heat credited to the heater); the heater line is computed. Your rate scales every dollar figure; your room temperature scales the heater column.
It uses whatever the tank loses, switching on only long enough to replace it. A 300 W heater on a lidded 75 in a 72 °F room replaces about 70 W of loss — 1.7 kWh a day, a duty cycle of 23 %, $9.22 a month. "300 W × 24 hours" is 7.2 kWh and $39 a month, 4.3× too high, and "assume it's on half the time" is still 2.1×. Every calculator on the first page of results asks you to guess the duty cycle; this one computes it from your glass, your lid and your room, with the same heat-loss engine the heater sizing calculator uses — that page bills the coldest night, this one the average year. Type your heater's rating in and the tool prints its real duty.
What uses the most electricity in an aquarium?
Whatever runs all day. A watt on for 24 hours costs three times a watt on for 8, so a 30 W return pump (0.72 kWh/day) costs more than a 60 W light (0.48 kWh/day), and the reef's four powerheads, skimmer and return outspend its lights in every row of the table above. The heater is the swing item: in a 65 °F room the lidded 55 above needs 2.8 kWh a day of heat, in a 74 °F room 1 — the same tank, the same heater, a factor of 2.7 — which is why the tool asks for the room's average in the cool months and the warm months separately and bills each for its share of the year. Lights come last in most freshwater tanks and first only in a high-light planted or reef tank with the heater barely running.
How many watts does each piece of equipment use?
The label beats this table, and a plug-in meter beats the label — but for planning, these are the ranges current products are sold at, priced at the middle of each range for the hours the device normally runs. The column to read is the last one: an air pump and a reef light are three orders of magnitude apart in watts and one apart in dollars, because one runs all day and the other a third of it.
| Device | Typical W | Hours | kWh / day (mid) | Per month | |
|---|---|---|---|---|---|
| Hang-on-back filter | 3–10 | 24 | 0.16 | $0.85 | small, but all day |
| Canister filter | 10–35 | 24 | 0.54 | $2.96 | older AC motors at the top of the range |
| Air pump | 2–5 | 24 | 0.08 | $0.46 | and it raises evaporation, which the heater pays for |
| Return pump, AC | 25–80 | 24 | 1.26 | $6.90 | the reef's biggest 24-hour line |
| Return pump, DC (controllable) | 15–50 | 24 | 0.78 | $4.27 | at the speed it actually runs, not the rating |
| Powerhead / wavemaker, each | 5–35 | 24 | 0.48 | $2.63 | reef tanks run two to four |
| Protein skimmer pump | 10–40 | 24 | 0.6 | $3.29 | in the sump, so its heat counts |
| Freshwater LED light | 10–60 | 8 | 0.28 | $1.53 | a 4-foot planted fixture at the top |
| Reef LED light | 60–300 | 8 | 1.44 | $7.89 | per fixture; at the intensity set, not the box |
| Heater | 25–300 | 24 | 3.9 | — | rating only — it draws the loss, see above |
| CO₂ solenoid | 2–5 | 8 | 0.03 | $0.15 | on with the lights |
| UV sterilizer | 9–55 | 24 | 0.77 | $4.21 | run continuously when run |
| Chiller | 150–500 | 6 | 1.95 | $11 | compressor duty cycle — the heater problem in reverse |
Spec-sheet ranges for current products, mid-range × usual hours at 18 ¢/kWh. DC pumps and dimmable LEDs draw what they are set to, not what the box says. The heater row has no cost because its cost is the tank's loss, computed above, not its rating.
How much does a reef tank cost to run?
More, and for two reasons the freshwater table doesn't show. The 120 gal mixed reef, open top above uses 7.6 kWh a day — $41 a month — and the pumps are 49 % of it: a return pump, powerheads and a skimmer at 155 W between them, all day, outspend 250 W of light on 8 hours. The open top would make the heater the other big line — evaporation from that surface is 138 W of the 222 W it loses in a 72 °F room, 5.3 kWh a day to replace — except that the pumps' 155 W ends up in the water and covers most of it, leaving the heater 67 W and 21 % of the bill. That is the reef's quiet economy: its circulation is its heating. It is also why a reef in a warm room needs a chiller, and a chiller is the expensive line, since a compressor removing 155 W of pump heat plus the lights' share runs a duty cycle exactly as the heater does, in reverse — the tool's "timed" line takes it at the hours it actually runs.
How do I cut the heater's cost?
Reduce the loss; the heater follows. A glass lid is the cheapest energy purchase in the hobby: on the 75 in the 72 °F room it cuts the loss from 170 W to 70 W, 2.4 kWh a day, $158 a year at the average rate — and more in a colder room or an open-top reef with a fan on the sump, where evaporation is the biggest single line. After the lid: foam board on the back and sides of a tank against an outside wall; a tank in the warmest room rather than the basement; and a lower target if the fish allow it — every degree is a fixed number of watts. Submerged pumps are not waste, incidentally: their heat goes into the water and the heater does that much less, which the tool credits.
Every watt the tank sheds warms the room, and in the heating season your furnace makes that much less. If the house is heated by electric resistance, the tank heater's winter cost is close to zero — the same kilowatt-hours would have been bought anyway. With a gas furnace at $1.50 a therm (29.3 kWh) and 80 % efficiency, the furnace supplies heat at about 6.4 ¢ per kWh, so the tank's heat really costs the difference — 12 ¢ rather than 18 ¢ — in winter, and the full rate in summer when it competes with the air conditioner. A heat pump sits in between. None of the calculators mention it; aquariumscience.org does, and is right.
Is a fish tank expensive to run? For scale
A typical refrigerator uses about 1.2 kWh a day — $6.75 a month at the average rate. The lidded 10 and 29 gallon tanks above use less than the fridge; the 75 gallon planted tank about the same; the open reef 6.1 fridges. Rates vary more than tanks do: 18 ¢ is the US average, New York is near 27 ¢ and much of Europe is higher again, so type your own — it is on the bill as the per-kWh line, and every figure on this page scales with it. What the tank does not change is the standing charge, which you pay with or without fish. A reef's other running cost, RO/DI water, is on the RODI guide; it is smaller than the electricity for most systems.
Why is my aquarium's electricity bill higher than the calculator says?
Usually the heater, for one of three reasons. The room is colder than its thermostat setting where the tank stands (a floor by a window in January is not the number on the wall); the top is more open than "lid" suggests — a hinged glass lid with a cut-out for the filter leaks a good share of the evaporation; or a fan is running across the surface for summer cooling and left on. A plug-in energy meter costs less than a month of the difference and settles it in a day. Beyond the heater: an old canister or hang-on filter draws its rating continuously; a "40 W" LED fixture at full output on a 10-hour timer is a 24-hour 17 W device; and a chiller, if you have one, is a compressor whose duty cycle is exactly the heater's problem in reverse.