Virtually every spa I have sold in the past 25 years has had a ring for the first few weeks - up to about the first month.
It comes from YOU.
Don't worry about it - it will go away over time as the tub deeeep cleans your pores from your neck to the bottoms of your feet. Keep wiping it off with a soft cloth, and think of all the people in India who don't have a hot tub, OR a soft cloth to wipe it with.
Yes the pH wanders upwards a bit. Add "Spa Down," or "pH/Alkalinity Decreaser" until it is in range again, and enjoy your tub.
I have suggested that people do a one-time water change at the end of the first month of ownership. I don't know if it would be worth it or not with the ACE - since you have to soften the water (pillow) and add the salt again. But consider it: you will love the feel of the second tub of water, I promise, and it does get easier to take care of the tub as time goes by.