I like the<u> Pinpoint ORP packets</u>. http://www.atlantareefclub.org/forums/images/smilies/smile.gif" alt="" />
In general, ORP calibration is often not necessary, and some meters, even very good ones, cannot be calibrated.
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[B]Randy Holmes-Farley[/B]
[B]
[/B]Randy is a PhD chemist. For lack of more definitive guidance, I trust him.
I used ORP in R&D and fought the variability issues, as well. The probes take a while to 'settle down' when placed in new solutions.