Actually, I have the best water for my tub with PH 6.8 and ALk really low. Using baking soda I get the PH to come in at 7.6 and my alk to about 130 - 140. I usually get my PH in line and don't worry about the alk.

My PH and alk don't drop for weeks and when PH hits the 7.2 mark, I adjust again and the cycle starts again. My pool Alk stays pretty constant and I use borax to raise PH.