I've been doing BBB on a plaster pool built in 2004 since 2006. Every year I would go through a big bag of baking soda and a couple of gallons of MA to hold ALC at 70 and keep the pH between 7.6 and 7.8. pH would hit 8.0 and I'd knock it down to 7.5/7.6 and then I'd need some baking soda.
This year I decided to do an experiment. After opening and adjusting to ALC = 70 and pH = 7.6, I just let the ALC and pH alone to see what the 'natural' point was. After a few weeks, it settled at ALC = 50, and pH is rock solid between 7.6 and 7.8. The water is crystal clear and is more 'eye-friendly' than it has ever been. It's stayed right there all summer. My jug of MA and baking soda bag are untouched since May.
The only corrections have come from about three weeks on pucks (in one week intervals) when I was travelling (CYA went from 30 to 40, as planned) and a record amount of NJ acid rain. Our rain is below pH 6.8 and it takes three drops of Taylor Base demand reagent to get to where I can read it. Normally I would use some well water (my metals are zero, and I have to add calcium) but this year I haven't. Well water is pH 7.1, I think.
So, I repeat, what's wrong with ALC = 50 in my case? It seems perfect to me. CSI is at -0.23 which seems fine. Absent any good argument to the contrary, I plan to leave it there.
Full test results, since someone will ask:
FC= 4 (before last night's LC dose)
Testing done with Taylor K-2006 except CYA which is the larger sample TFT test.