missusmacd

We have an Australian SCS Spa with a Balboa 501 control panel. I was advised by the supplier to leave the spa on Standard setting but we are infrequent users and our electricity bill has doubled ($2.40 to almost $6 per day - spa is inside). What is the most efficient way to use the spa and maintain temperature at 34°C? I do not understand the difference between Standard, Economy and Sleep modes as the best setting, and the manual does not explain clearly how to set the system for efficiency.