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Re: NO3 testing

>Date: Thu, 16 May 2002 10:38:46 -0500 
>In-reply-to: <200205160748.g4G7m2M28470 at acme_actwin.com> 
>References: <200205160748.g4G7m2M28470 at acme_actwin.com>
>Sorry, Philippe, but no.  The "if some is good more is better"
>philosophy does not apply here.  For maximum accuracy you should follow
>the directions that came with your test kit exactly.  The azo dye that
>is formed is not very stable and if you wait too long the color will
>begin to fade as the dye degrades.

For what its worth, I use a Salifert NO3 kit and the longer I let the
sample sit the pinker it gets. The instructions say wait 3 minutes after
which time there is no color at all. If I let it sit around for an hour
or so it turns a little pink.

Anybody have any experience with Salifert kits? Are they reliable? I
guess I need to mix a sample of water with a known NO3 concentration to
determine if the thing works correctly.