Bluelab pH Pen Calibration

Hello!

I had been using a liquid pH test kit for years and finally decided to splurge on a pH pen. It is definitely more convenient than the drops and I am glad that I did it. I do have one question about the pH pen, though, and I am hoping that some of you with more experience can help me out.

Whenever I calibrate the pen, I start by using the pH 7 calibration solution as directed. Usually when I put the probe in to this solution I get a reading at 6.9 or 7. When I put the probe into the second solution, the pH 4 buffer, I consistently get a reading of pH 3.8. Once I hit the calibrate button again to complete the calibration process, it sets the reading to 4 as it should. If, however, I go through the calibration process again, I still get a reading of pH 3.8 with the pH 4 solution. The other solution will read as pH 7, but the pH 4 solution will always read as 3.8. I have tried this out multiple times in a row with fresh calibration solution each time and still get the same result.

Is this normal, or should I see about getting this pen replaced under warranty? Perhaps it is an issue with this batch of pH 4 calibration solution?

Soak the probe in kcl solution for 24hours and try again, also transfering from one buffer solution to another without rinsing the probe in water can corrupt the reading and solution.

Just a couple of ideas, my bluelabs normally dead on once ive kcl soaked and calibirated.

Discard calibiration fluid after use, dont pour it back into the bottle.

Kingrow1 said:

Soak the probe in kcl solution for 24hours and try again, also transfering from one buffer solution to another without rinsing the probe in water can corrupt the reading and solution.

Just a couple of ideas, my bluelabs normally dead on once ive kcl soaked and calibirated.

Discard calibiration fluid after use, dont pour it back into the bottle.

Click to expand...

This was what I was thinking.

Thanks for your input, folks!

Yeah, I had soaked the pen for 24 hours before, I always rinse between solutions, and always discard the solution after use. I think it may have a bit of an issue. Hopefully I can find the receipt!