[quote=Jakebear]Marie -- Evan

Thanks for the info.

The weather has been crappy here in PA so now's the time to do this --- I have a supply of Stain Free and Metal Free (Natural Chemistry). As soon as the CL gets down to between 1 & 2 ppm I'll do my thing. With "Ernesto" coming up the coast we probably won't be swimming anyway (even though there is no restriction).

I was in another Chemical reference book today --- they said the same thing you did Evan so perhaps you use the same book
Only reference I used was what was stored in my head....nice validation that the stuff I said was actually correct!
I still can't get over my 0 iron and copper especially the iron.
If you have stains in your pool then you probably no longer have metals dissolved in the water....they are now precipiated out as stains. The ascorbic acid (or other reducing agent) will cause the stain to convert to a form that will dissolve back into the water (It changes the oxidation state)....and the stain vanishes but now there are metals in the water! This is where the sequesterant comes in.

FYI, NaturalChemistry's Metal Free is a chelating agent (EDTA) while Proteam's Metal Magic (HEDP, a phosphonic acid derivative) is a seqesterant. EDTA has a ring structure HEDP does not.
To confuse matters even more, sequesterants are measured in how well they seqester a particular metal by their "chelation index" for that metal!
 The Taylor kit doesn't lie --- Even though one of the people I work with had an explanation wanting to know what kind of Iron the test was for????
The Taylor test uses Tripyridyl-s-triazine which tests for Fe(II)...Fe is the Chemical symbol for iron. The (II) refers to it's oxidation state.
There ARE different oxidation states of iron, Fe(II) and Fe(III).
Since Taylor sells the K-1716 kit for pool water testing I figure it is for the "right kind" of iron.[
Yup!
/quote]
Isn't chemistry FUN!