Blimey, what's it matter to you?
I've done the math on my tank, even over estimating how much the heater is on (my room is ~75 degrees so my heaters spend a great deal of time off) my tank only costs between $7 and $10 a month to run. Most FW tank equipment draws very little current, only your lighting and heaters draw anything of significance and they don't pull much than a few mid to large sized light bulbs.
