Here is a very simple simple way to figure it out.
For instance my tank consists of the following.
60watt 1300gph return pump
216watt T5 lights
aquaclear 50 powerhead 12watts
some small air pump (idk maybe .5watt)<<neglidgeable
First things first, you need to know your energy supplier, mine is NYSEG and it costs me roughly 10cents per Kilowatt Hour DELIVERED. It is important to add the delivery and supply fee together.
Moving on we need all our units in SI and time related. They have to match the energy supplier which is kWh.
To do this you need to first move all your units from watts to kilowatts, this is just a factor of 1000. We now have
You then need these time related, mult all these numbers by 1hr.
We now have
This means if we take our heater, and run it for 1 hour continous it will use .3kw, which would cost us .3kWh X $0.10 per kWh (the kWh cancel out since it is in the numerator and denominator) and your left with $$$$, which is only 3cents to run that heater for 1hr on that day. If it costs you 3 cents per day, obviously mult by an avg of 30days and that is what it costs per month 90cents month.
For my tank i estimate and know the following
.3kWh my heater is prob on for 3 hrs combined out of the 24hrs in a day
.060kWh my pump runs for 24hrs day everyday
.216kWh my lights are on for 6hrs a day
.012kWh my power head is on for 24hrs a day everyday
Calculating my tank costs from the heater being estimated i now have
.3kWh x 3 x .10 cents = $0.090
.060kWh x 24 x .10cents = $0.144
.216kWh x 6 x .10cents= $0.1296
.012kWh x 24 x .10cents= $0.0288
total= $0.3924 a day for my tank
$0.392 x 30 days = $11.70 month for my fish tank.
I never really watched my heater so that could be on more or less then i think.
The people with these chillers, A/C window units in summer, skimmers, huge pumps...etc better sit down