I'm not sure if this is the correct section so mods please feel free to move it.
I have a 1 year old gunite built in. Last year we closed the pool at a balance 7.5 ph. This year when we opened it the PH was 10 and crystal formation formed on the entire gunite surface. It felt very sharp on the feet. At any rate I lowered the PH to approx 6.8 and after a week plus brushing things returned to normal. I understand this PH drift happens with newer plaster pools and it should calm down over time, however, I want to avoid this problem next year. So I was thinking to power the PH down low to compensate the natural drift upward. And that is my question, how low can you go safely at closing to avoid this problem? Thanks in advance.