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Sera iron test -- sensitive and easy

At 03:48 AM 4/13/99 -0400, Daniel Boyer asked:
>I finally got an Iron test kit (Sera)... I tested my water and it showed 0
>mg/l so I added some Tetra Flora Pride...waited 12 hours and retested... got
>a 0 mg/l .... added some more... tested a few hours later and it still shows
>up 0 mg/l!!!!  Whats the deal???  My plants can't be using it that fast...
>Some one please help me.

Well, Daniel, it can depend on how much deficit of iron your plants have
and how much they are willing to grab up from the water and sequester
before they will leave some to be measured.  IMHO, you definitely picked
the right test kit.   There are a couple of tips to using it however.   If
you get a reading less than 250ppb, I recommend you use 25ml of water for
the test, not the 5ml in the instructions.   Secondly, at low
concentrations one drop of indicator is plenty.   Thirdly, read the tube by
looking down from above.  Note very carefully the color before adding any
indicator, then add indicatork, wait three minutes, and look again.  The
faintest pink tint means about 25ppb.  That to me is a very sensitive test,
and when you use only one drop of indicator, you get about 240 tests from a
$12 kit.   That means only about five cents per test.  I like the Sera iron
test kit so much that I am considering selling it.   If you are interested
in more info on this, contact me offlist.  BTW, my understanding is that
after 1 minute you see only unchelated iron, as the sample ages, iron is
liberated from chelating agents and adds to the color shown.   If anyone
can confirm or refute this I would be most interested.

Dave Gomberg, San Francisco            mailto:gomberg at wcf_com