Welcome to our forum.
Out of curiosity, what sort of tub do you have? In ground, acrylic? I only recently learned that water hardness is irrelevant if you have an acrylic shell and the tub isn't near concrete where pitting would be a concern.
CH 100-150 is a good rangeI like Alk. around 80-100ppmI have areas around here where some tubs take 28+ ounces to drive alk. and pH down...if you don't like using so much product you can pick up a gallon of acid at Menards... I know there is conversion charts on the web for calculating how much to add