my “normal” Greisinger electrode did not work properly with a conductivity of 20 uS. Then I found in the book by HJ Krause “aquarium water” following trick: a little KCl-3 molar add to sample water.
A cross-check with an expensive WTW device / electrode then was only a difference of 0.1 PH. I think that’s ok.
Has anyone tried it too?
Best regards
Arno