Glad you got to the bottom of it Susan (and Sailor) and a cheese for both of you for the discovery
. The Extech ExStik is, as far as I can find, the only pH tester anywhere near it's price range with a flat electrode that can measure both liquids and solids. I've seen a few probe sensor that can do solids they leave a mark (hole) and they're $200 and up. For that reason we've decided the pH100 is the only tester we are going to carry. I still have my beloved Oakton pH2 (actually it's my 2nd because the first one had a cracked housing) and it is satisfactory, but for $30 more the Extech is worth it.
By the way (and just slightly off topic) if you're really interested in seeing what's going in your cave as far as temperature and %RH are concerned you may want to look at a humidity / temperature USB datalogger.
Extech sells one and so does
Lascar for the same price. I've used both, and while Extech makes a great pH tester the Lascar datalogger is in my opinion superior and has a better data downloading interface. The data you get over a longer time interval can help diagnose problems.
