We have had our tub for 6 months now and the power usage is much higher than we expected. Our power bill has gone up about 15 -18 kilowatts per day over last years, which is about double what we were told. It is a 240 volt system. We use the tub 1-3 times a week, usually bringing the temp up from 95 degrees to 103-104 a few hours before we want to use it and then turning the setting back to 95 when we are done. Is there a more effecient way of running this thing? Should we be setting the none use temp lower? Any suggestions?

I assume you're taking KWH per day not kw per day.

That would mean you're getting billed about $80 more per month electricity wise right?

What brand of tub is it, and is your spa cover installed when it's not in use, is it self contained or contractor installed or what?

More info would help.

Correct, KW per day. It is a Mountain Springs tub, that is self contained, which sits in a gazebo. It is insulated with the typical spray in, and we always have the cover on (except when adding chems or in use of course)
We are now turning the tub down to 85 degrees when not in use, to see if that brings down the daily average.
My main concern about playing with the temps is I thought I read somewhere that bacteria grow best in temps between 70-90 degrees, but I can't confirm that.