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Re: Aquatic Plants Digest V3 #1036

At 03:48 AM 5/18/99 -0400, Dotson, Sam said:
>I'm looking for test kit recommendations for Iron....

The only one I would seriously consider is the Sera kit ($6 from Pet
Warehouse petwhse.com).  Then you need to use my copyrighted directions:


The first trick in using this test is to figure out HOW to use it.
The instructions do not say exactly how to compare the tube with the
printed color chart.  Here is the method I have devised:

Use a plain white surface which is lit from the side, preferably by
diffuse daylight.  I happen to have a nice white Corning Pyroceram
counter saver in just the right place.  Read the tube by looking
down from above and observing the color of the fluid in the tube.
Read the chart by tilting it enough that it is free of shadows (if
set horizontally, shadows may be caused by wrinkles in the paper).

The Sera test kit has its first level of measurement at 250ppb
(parts per billion, ug per liter).  An easy way to extend the range
is to use five times the 5ml of water the instructions call for.  To
take 25ml of water, just extrapolate the existing scale on the
cylinder which goes to 20ml.  This will mean that the faintest
printed pink color corresponds to 50ppb of Fe++.  And when measuring
low concentrations, use only one drop of indicator.

You will notice that the faintest printed pink is actually rather
strongly colored.  It is possible to detect a bit of pink that is
quite a bit fainter than the faintest printed color.   Although it
is difficult to quantify such low levels, they can be used to
detect the presence of SOME iron.  One can wildly extrapolate
values to such faint colors, but they should not be relied on.

As delivered, the test appears not to measure chelated iron.
However, if the tube is left alone for a protracted period, the
color deepens.  It is my interpretation that this represents the
indicator dye in the test chelating the Fe++ in preference to the
chelating agent in the aquarium water.  If this interpretation is
correct, then by waiting for a protracted period (a few hours), the
total iron (chelated and unchelated) can be measured, using the
same techniques as are used in the basic test.

Dave Gomberg, San Francisco            mailto:gomberg at wcf_com