Hi Danndy! Â FWIW, I have a 400 gallon tub, 7 1/2' square. Â I use it daily/every other day. Â On occasion it gets used twice the same day. Â We probably average about 20 - 30 minutes per use, plus the time it's open to chlorinate. Â My water level drops 1" - 1 1/2" inches per week.
First couple weeks I thought it was leaking but it's just evaporation. Â Hopefully that's the case with yours. Â Yokeman is right about also losing water when you exit the tub. Â That amount is greater if you wear a suit (holds water like a sponge.)
BTW, I have a friend in Michigan who just bought a Siberian. Â I got to see it last week and it's a great tub. . .Congrats!