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Milwaukee PH pen?

For about a year, I have been using the Oakton pH Wand ($93.50, Part No.
U-35624-35 from Cole-Parmer) with a replaceable, single junction electrode
($72.00, Part No. U-59000-51).  This has resolution of 0.01 pH unit, an
accuracy of +/- 0.01 pH unit, 3 point calibration (4, 7, 10), and automatic
temperature compensation.  I calibrate it monthly and this has proven rock
steady for me.  Since my color perception WRT test kits is poor, this was
worth the investment for me.

I have also been using a Hanna Instruments HI-981411 pH Controller ($110
distributed by Automatic Aquarium Systems) with the HI1001 electrode ($95,
also AAS).  This has resolution of 0.1 pH unit, an accuracy of +/- 0.2 pH
unit, 1 point calibration, and no temperature compensation.  Since Iím
controlling at pH=6.8 and constant T=78 F, the single point calibration does
not disturb me.  I have learned to calibrate the controller versus the
checker when I run my weekly water chemistry.  The set point of the
controller does not seem to drift at all, and I donít think the calibration
of this meter drifts much either.  However, the properties of the electrode
change as a function of time in the water (from deposited organics).  I have
learned to clean the electrode monthly.

Joe K

(I have no financial interest in any company)

C-P	www.coleparmer.com
AAS	http://www.automatedaquariums.com/index.htm