So long as you don't use any acidic sources of chemicals, such as Dichlor (or Trichlor) or non-chlorine shock (MPS) and you are very careful with adding acid, then a lower TA is OK. See if you can get to a TA of 50 ppm with a pH of say 7.7. That would be a tad better with a little more buffer "just in case". There are some other spa users that are in the 50-60 ppm range and I think one was around 40 so what you are experiencing is not unusual. It's just additional proof of how a higher TA leads to a faster rise in pH and that the use of bleach is actually pH neutral.

The other thing you could do is use 50 ppm Borates in the water, but that probably won't lower the amount of acid you have to add over time, but it will make such acid addition less frequent and slows down the rate of pH rise. Also, I'd recommend the Borates if you plan to keep your TA very low because it will help reduce the amount of pH rise that occurs immediately after adding bleach (it drops back down as the chlorine gets used up).

Do you have pretty substantial jets or other sources of aeration? Do you keep the spa covered when not in use (I would assume you do)? Are you using Clorox Regular unscented 6% bleach or are you using another brand?

Richard

You can switch from chlorine to bromine or vice versa upon a fresh drain/refill. You can even switch from chlorine to bromine by simply starting to use bromine tabs and adding sodium bromide to create a bromide bank. You cannot, however, switch back from bromine to chlorine except by changing the water.

You can also use chlorine as your shock in a bromine tub, instead of using non-chlorine shock (MPS). The chlorine simply reactivates bromide to bromine, just as MPS would do. That is, once a bromine tub, always a bromine tub, at least until the next drain/refill.