re: Stupid Question

To: Aquatic-Plants at actwin_com
Subject: re: Stupid Question
From: Chuck Lawson <lawson at junglenet_com>
Date: Thu, 07 Nov 1996 16:12:35 -0600
Michael Eckardt <mike at odg_com> wrote:

>This procedure agrees with my (non-Sandpoint) instructions, except perhaps,
>that I am using a 4.01 standard instead of the 10.0.

So you calibrate at 7, and then insert it in the 4.01 solution and set the
slope?  This seems to me to make more sense, if one is targeting a pH range
below 7 instead of above (I assume setting the slope at 10 would be
oriented more towards the reef tank crowd).  I wonder if mine could be set
accurately with a 4.01 solution, or whether they are specificly designed to
have the slope set in one direction or another?

>As an aside, how does one clean a probe effectively and safely?

Good question :-) Marque had some advice in his message that sounded fairly
good.  I was surprised that I had little or no gunk on the surface of my
probe after sitting in the sump this long -- I just wiped it with a damp
paper towel, and didn't really see any debris or discoloration on the towel.

>Also, I read somewhere that the life of a probe is 6 months. 
>What are your experiences? 

I've heard that on-and-off over the years, and I expect that it is true,
but dependant on the amount of accuracy one wants to obtain.  If I can get
a +/- .2 degree of control over the pH with it (by moderating the CO2
injection), I'm fairly happy from a practical standpoint.  In more exacting
or laboratory applications, six months may well be the end of the
functional life of a probe. Just comparing my readings with a reagent test,
it seems to be (after significant neglect) pretty close, given the accuracy
of the average reagent test (or at least my ability to read it accuratey
:-)  I'd be interested in hearing anyone's experience with how long you can
get a "servicable" range of accuracy from them.

My wife has had some experience in medical applications of pH probes, but
for some reason I've never asked her what the lifespan of their probes was
-- I'll have to do that.  From what I vaguely recall (5 - 6 years ago), it
sounded like they were replacing quite a few of them sooner than every six
months just from accidental damage rather than wear or inaccuracy.

- Chuck