a 1200 is 30W for a 250L tank, and its in the high range for canister filters for power useage.
The eheim 2075 uses just 16W for up to 600L tanks
my fry tanks run on air pumps (one at 5W for 2 tanks) my smaller HOB filter runs at 3W, plus 2x 50W heaters (which are not on 24 hours a day). all tanks have 3 sided insulation i'd guestimate about 3-4 hours a day heater is on
work out how much your tank costs....
take the wattage of the item, times it by how many hours a day it is on, divide it by 1000 to get useage in KWH per day, times it by 30 for monthly usage.
grab a power bill and work out the cost by multiplying your result by whatever you are paying per unit (use the higher amount to make your argument stronger. )
and voila.... perfect excuse for another tank....