High pH

Apologies in advance, but I am an oldy (70 years) and my knowledge of the etiquette for forums is very limited. I have a problem with my pool in that the pH keeps going high >8.0 despite adding numerous litres of acid. The acid brings it down to the acceptable range, but within a week or so, the pH is back up high (pool is not used much). Test strips indicate all other parameters are around normal except that the total hardness is high (>1000).

By way of background, my pool developed a...

High pH