pH "pen"

[jsheffel]

I am just getting started back up in the hobby after several years of not having a tank. I have one of those electronic pH "pens" that still turns on, but am sure that it is out of calibration. Can I rely on the distilled water I buy at the grocery store having a pH of 7.0?

[tray262]

there companies that sell a calibration media.

[The R/C Man]

My RO/DI water reads 7.0. Maybe that is a good starting point....

[dougc]

Was the probe kept moist? Every pH monitor or tester I have had recommended that the probe be kept in 7.0 solution when not in use. I guess you could see if it is still ok by calibrating it and then comparing it to another pH monitor or even a pH test kit. I don't know how long a pH probe lasts, but Neptune recommends replacing the ones on the Aquacontroller every year. A pH pen might be different, though, since it is only occasionally used.

[rayjay]

You need two calibrating fluids, pH 7 and pH 10 to calibrate.
If the tip has not been kept moist, it probably won't read correctly, even after calibrating.