if your tank is not a planted tank you might as well cut down on the lighting, especially if you are not even there to appreciate the tanks. another thing that you can obviously do is turn down the tank temperature to a minimal safety level. I have also known people to insulate the back and sides of the tanks to keep the heat loss down.
there are also other costly options that would help you save energy such as switching to LED lighting but that may cost you way too much initially.
like others have said, even with your equipment you are probably not responsible for the energy spike, but you can always take the steps that I have recommended and tell your parents about them, im sure they'd appeciate your effort to help them save money.