Lose of heat without the cover

[hottbpete]

I have by accident left my cover off the tub....ok my kids did.
The temp went down to 96.....it's jut under 30 degree here.  It was open for a few hours.  I am wondering if this is norma/  I was in the tub for an extended soak yesterday....2 hours and did not lose heat at all.  Main difference was I had the jets running the entire time I was in yesterday.

Any thoughts?

[Brewman]

Running the pumps to power the jets helps heat the water.  If your spa lost that much heat without the pumps running, then your spa water was loosing heat faster than the heater could replace it.  
 If it was windy out, that would further accellerate heat loss.  There is a lot of temperature difference between 104 and 30, and the greater the difference the faster the heat loss.  Be glad it wasn't below zero!