With TA of 120, you might not need any chemicals to raise pH. Sometimes just aerating the water, like turning on the spa or waterfall or pointing a return upwards so it breaks the surface of the pool, will push pH up. Where is the pH now, and where do you want it to be?
There's a nifty feature down near the bottom of poolmath. It shows the Effects of Adding Chemicals. Provided you have entered your numbers up above in the now column, it will show you approximately how much adding different chemicals will affect other readings.
16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!
Not sure where you got that, or what the discussion was, but Baking Soda is Sodium Bi-Carbonate. It's different than Soda Ash/Washing Soda.
Baking soda adds a lot of TA without doing much to pH unless the pH is quite low. Soda Ash raises pH much more as well as increasing TA.
As Richard said, you may not need to be adding things to increase pH. Most likely you should not. With TA 120, it should be rising anyway. What is the pH now??
Ph is a little on ht low side of 7.0 or so.