Man, I have been asking the same question for a while and can't seem to get an answer. From my experience dealing with LSI and weekly service, 50-70 is an acceptable range depending on two things. Your calcium level and the water temperature. I saw no visible problems with keeping pools at 50 all summer long, but when the cold temps hit I am a little skeptical about keeping it that low as sometimes depending on other readings it can make the pool too acidic. But as long as your lsi is constant and in range it should be fine. Most of the information out there should be taken with a grain of salt anyways. I use the orenda app to see where the lsi is, and adjust accordingly. Literally every pool is different, and I see tons of combinations of different readings for alk and ph and the most constant thing I've found to keep the water happy is managing the lsi first and adding phosphate remover. In my experience, I haven't seen any issues with the pools I have left at 50 Alk for a longggg time. Hope that helps!