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[AGA Member] Re: iron testers

I weigh in on the side of not testing for iron.

Depending on the iron test kit you use and depending on the kind of iron
suppliment you use the iron test kit results may or may not be useful to
anyone in particular for any given purpose at any particular time.  Now go
invest your money in that one!

Most of my experience is with Flourish and Flourish Iron.  Several people have
tested the behavior of Flourish Iron in their tanks and found this simple
behavior; it doesn't stay in the water very long at all.  If you want to keep
your plants well supplied with dissolved iron using Flourish Iron then your
best bet is to dose small amounts frequently.  I dose daily.  If you dose at a
lower frequency then the plants will be supplied in abundance for one day and
the rest of the time they will have to scavenge iron out of the substrate. 
When I switched from 1x or 2x weekly doses to daily doses I halved the amount
I dosed per week and the appearance of my plants improved.

If you use a strongly chelated iron (Fe-EDTA, Fe-DTPA, etc) then the test kit
results can be very difficult to interpret.  Unstressed plants can't or won't
use the chelated iron directly; only a very small and unmeasurable part of the
total iron is unchelated and actually available to plants at any one time. 
What you get out of the test kit is (ideally) a measure of the "storehouse" of
chelated iron in the tank.  The iron in that storehouse might become available
to plants later. It might be enough for your plants or it might not be enough
for your plants.  Only experience and observation can answer that question.

The iron in an earthy substrate (Flourite for example) may or may not ever be
available to plants.  The availability of substrate iron and the rate at which
it becomes available depends on the details conditions in your substrate. 
Furthermore, different plants have highly varying abilities to harvest iron
out of a substrate.  If conditions are right then the substrate can reduce or
eliminate the need for further iron suppliments.  If conditions aren't right
then the substrate will have no effect at all.  The amount of iron supplied by
the substrate cannot be measured with an iron test kit.

Whether your plants need an iron suppliment, how much they need and what kind
they need comes down to observation and experience.  Testing offers little. 
But then, testing isn't likely to hurt anything but your budget and your time;
if testing helps improve your observations then maybe there's a net benefit. 
Or maybe not.  How would I know?

Roger Miller
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