I have been using ph meter from Dick Smith (approx $ 90), but found them too
unreliable after a while, as probe is blocked by salt/oil in the brine.

We are now using a scientific version (approx $600), which has 2 buffer
solutions (4+7) to calibrate and the probe is always kept in demineralised
water. It gives us the brine temperature at the same time.
Hope this helps.

Knut Kammann
Lakelands Olives
Clandulla NSW