The only thing that will cause TA to go down it adding acid. If your pH is staying stable enough for you now don't change it but as chem geek and I said before, most SWCGs seem to exhibit the BEST pH stability with the TA at around 70 ppm and 50 ppm borate (with CYA at the manufacturer's recommended maximum) and there is several years of evidence in actual pools to back this up from various forums and other sources.