So given my fill water has a TA of 30 ppm, this is the value where it probably wouldn’t go below if I never added increaser?
It would still increase from there. Evaporation leaves TA behind, and then you add more with fresh fill water. But with TA 30 fill water, that should be a slow process.
And each acid addition will bring TA down. There's a simple rule of thumb for those thinking metric: Take your pool volume in hecto litre, replace the hecto with a milli, and that's the acid amount that will reduce your pool by pretty much 5ppm. Example: You have a 30000 litre pool, that's 300 hecto litres. An acid addition of 300 milli litres (full strength MA) will reduce your TA by about 5ppm.
I wouldn't go below 50. You want some buffering left for things going wrong. Acid container slipped, acid added instead of bleach, it has all happened before. Pool service who takes over while on holidays throws in a few pucks. Whatever.
One issue with pH 8 is that you don't know if pH is actually higher, unless you have a well calibrated electronic meter.
Australian standard AS 3634 for private pools wants pH to be not higher than 7.8. This doesn't make much sense as a standalone rule, for the risks with higher pH they are mentioning things like reduced chlorine effectiveness (which is only valid without CYA) or scaling (it's not pH alone, CSI counts). In the end it's up to you what to make of that, and that you understand what you are doing and potential consequences.
Another thing is that around pH 8, and quite pronounced above 8, FC loss to UV starts to become more significant, particularly at higher FC/CYA ratios:
OK, so I am a newbie. But, I’m ignorant of pH within Chlorine relationships. I can find very much data here on Chlorine/CYA, but what about pH? Basically without getting too technical……haha, (I’ve read Chem Geeks articles) I am trying to figure out the effectiveness of Chlorine at different pH...
www.troublefreepool.com
I usually let pH ride through winter up to 8. In summer, I usually keep it below 7.8, I need those acid additions then anyway to stop my TA from rising. TA usually between 70 and 90.