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Re: [APD] CO2 and pH control

If you can calibrate it at the two different points -- and
it doesn't take all day for it to settle in to a steady
readying -- and it doesn't wander badly over, say, a month
between calibrations, then there isn't much more you could
as of a probe new or old.

Generally when these types of probes get long in the tooth,
it becomes difficult to calibrate. They very slowly settle
in to a steady reading at one point, say 7.0, and when you
calibrate the other point, say 4.0, and then come back to
7.0, you need to read just the reading for 7.0. YOu go go
back and forth and the unit doesn't want to settle in and
hold.  When you tire of this, you order a new probe ;-)


--- "John T. Fitch" <JTFitch at fitchfamily_com> wrote:

> > Date: Wed, 14 Dec 2005 08:05:26 +0100
> > From: "Laith Arif" <laith at swissonline_ch>
> > Subject:     To: "'aquatic plants digest'"
> <aquatic-plants at actwin_com>
> >
> > Usual single point calibration is to 7.0, not 7.2. 
> Dual point calibration
> > is usually to 7.0 and either 4.0 or 10.0.
> >
> I have a question about the lifetime of my pH probe.  I
> bought a Milaukee 
> SMS 122 probe and controller in September 2002.  I was
> under the impression 
> that I would have to replace the probe after about a
> year.  But it's been 
> three years now, and it seems to be working as well as
> ever.
> Every few months, I check the calibration against Vital
> Sine pH 7.01 and 
> 4.01 solutions, and it's never more than 0.1 unit off. 
> Usually it's right 
> on the mark and doesn't need any tweaking.  As long as
> this is the case, is 
> there any reason to replace the probe?  Thanks.
> John T. Fitch
> www.fitchfamily.com/aquarium.html
> _______________________________________________
> Aquatic-Plants mailing list
> Aquatic-Plants at actwin_com
> http://www.actwin.com/mailman/listinfo/aquatic-plants

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