ExStik pH Meter

[bansidhe]

So, eager to work with pH, I bought an ExTech pH meter based on recommendation from people on this board.  This morning using 4 & 7 calibration solutions, I set out to calibrate.  Unfortunately, the ExTech read the 7pH solution as 5.97 and calibrated to that.  So, I removed the batteries , pressed On/Off button for ten seconds, replaced batteries and tried again.  I got the same result.  Out of curiosity, I tried the pH4 solution.  The ExTech measured that at 2.97.  It seems this meter is off by 1.03.  Though I would not trust this.  Is there anything I am missing?  Else I guess I will have to send it back.

[paulabob]

Did you calibrate the solutions in the order the directions gave?  I know with my meter, you start with the middle ph, then do the low, then do the high.

[bansidhe]

I followed the directions with the ExTech, I believe. I put the probe in the pH7 solution.  Then I pressed the calibration button.  The calibrated pH was 5.97

Is there something more I should have done?

[paulabob]

I don't know your meter, but with mine, you press and hold the calibration button for five seconds.  After that, the reading changes, and then you can place back in the solution and see that it "stays" (or mostly) at the new reading.  My instructions also tell me to hold the meter in the third solution for a few seconds before trying to calibrate (once I didn't, and it calibrated to the neutral ph instead).

Are you saying it calibrated to the 7 reading, and the meter shows that you calibrated to that on the meter, and then immediately changed the next time you used the meter?  10 minutes later, or when/what happened.  More details on your steps would help someone advise you (and hopefully someone who owns the exstik can chime in).

[bansidhe]

I let the probe sit in pH 7 solution for ten minutes.
I removed it and rinsed with water , drying with a cloth.

I then put it in a pH7 solution again and pressed the Calibration button.
The pH meter only read 5.97.  It did not change.. even when I pressed the \button.
When it indicated it had ended, then the pH of 5.97 remained. 

Should it not have indicated it to be pH 7?


Thanks

[paulabob]

Hmm, when you rinsed with water, was it distilled water?  I generally keep a bowl handy to clean the ph meter with in between readings.  Tapwater would mess with the meter - not permanently, but it does change its ability to read correctly.

[bansidhe]

Yeah....  Thanks for your help... but I returned it. Perhaps, the electrode got dried out or soemthing.

Anyway, I bought an Apera pH meter.  and THAT one seems to have calibrated just fine.  I'm going to use it my next make.

Fingers crossed!