Fuck around with an old fart and find out!
I won my battle with the gym operator who decided to make it his mission in life to thwart my efforts to have a 40C/104F Jacuzzi bath at 06:00 in the morning.
He didn't respond to me or to his general manager, so I pushed it up to the owners, and offered them an engineered solution, which they accepted and told the operator how it was going to be.
My solution was to top it off at night during closing, and proved that it would still stay in the designed operating range the next day.
In parting I pointed out that the grout was disappearing from the bath liner, which was a dead give away that the tank was running lower Ph than specified. I forgot my bottle to collect a test specimen, but will do so Wednesday for specifics.