I'm assuming you had the spa store test your water? I don't know how to get a TA reading of 139ppm.
I would test the soft water and then test the hard water, separately. This is what I did so I had an idea of how much of each supply to fill up the spa. My soft water had a CH of 0-10ppm, and my hard water had a CH of 280. I filled the tub with about 2/3 hard water, and the rest soft water. I ended up with a CH of 150. From what chem geek has posted, a CH around 150 will keep the foaming down. Other than that, it's not very important. My pH and TA levels were the same for soft and hard water from my well. You can't adjust the pH by using more soft water or more hard water. I would just try to get the CH between 100 and 200 and call it good.
When the tub is full, aerate the tub with jets and air controls. This will raise the pH to where it wants to be. I had a TA of 400ppm, and a pH of 7.2 on my initial fill. This doesn't make sense, since a high TA means a high pH. Well, after aerating the tub for 20 minutes, my pH went sky high, as it should have. I then added muriatic acid for the next 6 hours in small doses to bring down my TA. Add acid, aerate, add acid, aerate. It could have went a lot quicker, but I didn't want to overdue it, because it was my first ever hot tub water balance. I brought the pH down to 7.8, and my TA was at 90. Today, about 6 weeks later, I am sitting at a pH of 7.6, and a TA of 50 to 60.
I read an article that said soft water was not good for your tub, but in another forum, the boys said it does not have a negative effect on your tub. A low pH or a high pH will cause problems, from what I have read.
I thought you bought a test kit??