If you are talking about the Rapidtest soil testing pH probe (generally under $8 US), it does not work for this application.

You need a proper pH tester for testing water and solutions (digitals start approx $35). I'm told that an inexpensive aquarium test kit will work also.
crabbyback Reviewed by crabbyback on . PH meter questions I recently bought this pH meter and have some questions. Its the one thats electronic by Rapitest. 1. Does it need to be calibrated? I feel like that's a stupid question but I wanna makes sure I'm doing things properly. 2. If it does, I only have the ph 7.0 calibration fluid, is this sufficient? 3. How do I do this exactly? (I've researched a little bit but I'm still confused) 4. ANOTHER really dumb question I have is does it have an on off button/function? Rating: 5