I know there a few variables such as ambient temp, aquarium size, temp setting in the aquarium... But does anyone roughly have an idea how long per day a heaterstat would be on. Im just trying to get a feel for energy costs using the PFK calculator and the potential 40% increase in elec prices this year. I am estimating a possible increase to Â£0.17/per kWh. I took a rough guess and thought maybe 8 hours a day?? Water cools down quite slowly though... maybe im way off, hope so because the total aquarium running bill is looking like Â£800 odd per year. I was thinking of reducing light on period from 10 to 8 hours...is that fairly ok for plants? Im thinking it is, but just want to get some views.