phosphate, iron and diffusion coefs.

> From: tmarch at primenet_com (Todd March)
> Date: Tue, 13 Aug 1996 18:34:33 -0700
> Subject: About Red Sea Test Kits
> On August 13, John Lobingier asked about Red Sea's Phosphate and Iron test kits:
> I have used Red Sea's phosphate and iron test kits. The phosphate kit is
> very easy and accurate, and matches the readings I get from Dupla's. The
> colors can be a little hard to read in the .15-.30 range, but it is
> acceptable, and since the Red Sea kits are becoming easy to find in stores
> throughout the world, I give it the thumbs up. The packing is innovative
> and great--the box unfolds as necessary to become a handy little test tube
> stand, so tests are fast and neat.

The Red Sea phosphate kit is ok, but the range is a little high for what 
I use these things for.  All kinds of ugly things happen in reefs at 0.3 
mg/L PO4.
> I have had trouble getting ANY reading with Red Sea's iron test kits,
> including their most recent revised issue, that comes as part of a "Plant
> Care Kit"--which includes a great and accurate CO2 test (again, always
> matches my Dupla CO2 test). I keep my Fe levels around .10, and a lot of
> tests have trouble with this low of reading, short of Dupla, LaMotte and
> SeaChem. For iron testing, I would recommend staying away from Red Sea;
> though I have talked to other aquarists that have have had no problems with
> this same test, so...?

Hach makes several fine iron test kits, using a number of different 
chemistries.  Several will work at the range of iron concentrations that 
FWPTs are maintained.

> I have had good luck with Sera's Fe test, but the reagent stinks to high
> heaven, and will stain your hands reddish-purple.

That would be the Ferrozine chemistry.  It is one of the most sensitive 
solution iron methods, and with even a cheap spec like the DR/2000, you 
can read down to 2 ug/L (2ppb.)


> From: "Olive K. Charlsey" <achaudh at emory_edu>
> Date: Tue, 13 Aug 1996 22:02:17 -0400 (EDT)
> Subject: Ions
> Hello,
> 	A definition: Current is defined as the movement of charge, 
> whether that be electrons or ions.
> > Which ions are more mobile? Perchance, is there a table giving
> > mobility parameters?
> 	Well, really, their mobility is dependent on their charge and 
> their masses. Table? Well, you don't really need one... 

And hydration and hydrolysis of first-shell waters, etc.
In any event, what the questioner wants to know or have is a table of 
diffusion coefs, which I don't have in front of me right now but could 
get if there is genuine interest.

Although it is not apparent in the chopped up replies, the original 
statement was regarding conductivity, that various ions have different 
mobilities (even beyond charge and mass of the ion itself, because 
hydration plays a major role)

Diffusion coefficients and ion mobility in an electric field are related.
Of course this charge business plays a dominant role in the latter. 

> 	However, to answer your question... O2 and CO2 diffuse rather 
> slowly in and out of the substrate - as do other nutrients.

Thanks for that, the answer is "slowly."  Its cafe au lait time.