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Re: pH Monitor

> Date: Mon, 22 Jan 2001 00:39:14 -0700
> From: "Chuck Gadd" <cgadd at cfxc_com>
> Subject: pH Monitor
> Ok, just purchased a used pH monitor.  I have no idea how old the probe is, so I
> won't be surprised or dissapointed if I need to replace it.  I'm going to get
> some calibration fluids this week.   Right now, I've got the probe in my 
> sump tank, and the meter reading seems to be jumping thru a range of values
> from 6.6 to 6.8.   I know that the values aren't really usable until I
> calibrate, but is the jumping values a sign that the probe is toast?  I 
> did notice that today when doing a water change, the probe reading climbed, as
> I'd expect since I add new water into the sump.     And by tonight, the values
> were back down to the 6.6-6.8 range, so it seems to be functioning somewhat.
> What calibration fluids do I need?  I see that they sell a 4, 7, and 10.

I have all three. I soak a dirty probe in the 4 to let the acid wash out the
worst of the crud/scale. I use 4 and seven to set the gain and midpoint.
Then it's really nice to see how linear it is by checking at 10. Most are
not exactly on, so you can tweak the two settings to get the best average,
or to get the best accuracy in the range you normally use (just below 7?). I
think anyone can get by with buffers for 4 and 7. 10 is gilding the lily for
an extra fractional point.

>  Also,
> do I need to be concerned about adding grounding probe?  I seem to recall someone
> mentioning that stray voltage from pumps and/or light ballasts could effect the 
> reading.

I have no controllers, but I believe it is true. The pH probe is just a
battery, and you are asking for precision measurement of tiny voltages. It
needs no help to be way off.

> And if I do need to replace the probe, any recommendations on where to find
> the best price?

Sorry, I've never had to replace one!


Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

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