I've been in the same boat as you...my pool's TA was always dropping below my targeted 80. If I tried to increase it, my pH went up. Then I'd add acid which dropped my TA - an ongoing cycle that I detailed here: http://www.poolforum.com/pf2/showthread.php?t=6998

Chemgeek gave me some insight and, after some experimentation, it appears my pool likes to live at TA of 50-60 and a pH of around 7.7-7.8. So, it appears I'm in line to increase my CH to keep things in balance.

Hopefully, Chemgeek or some of our other chemistry gurus will give you some specific advice for your pool.