I've been having high pH issues for some time, and my probe tests out fine in the 7 and 9 pH solutions.
Mine gets as high as 8.75, but the corals and fish seems to like it just fine.
At night it drops to about 8.4.
And that's with a calcium reactor and a nitrate reactor running, which both knock don the pH level, so I don't want to know what it would do without.
When I started the tank, I had a hard time keeping the pH up, but after about a year, the pH slowly started getting higher.
Apart from more aeration, there doesn't seem to be much that can be done.