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Re: My tank can't get enough iron!
Tom Wood wrote, in reaction to a post from Greg Morin regarding the dosing
and detection of Iron in the water column:
"This seems like a case of the dog chasing its tail. It's my understanding
that a properly constituted trace element mix is made such that every trace
element is present in the same ratios that they are used by the plants. So,
if all the iron is used up by the plants (and not lost to other processes)
then all the other trace elements will be used up as well, because they are
used in lockstep with iron in the ratio they are present in the mix and in
the plants. Isn't that the underlying assumption to using iron test kits in
the first place? That since iron is most easily tested, it is used as a
proxy to indicate the levels of all the other trace elements? If an iron
rich supplement is used just to get a reading on a test kit for iron,
doesn't that make dosing the other trace elements a shot in the dark again?
It seems to me that a coupled set of products is needed - One that provides
iron and the other traces in the correct ratios, and a test kit that
properly reflects the iron level so that we know that the dosing for all the
trace elements is reasonably correct."
Mmmmm......... I think that perhaps you might want to revisit some basic
plant nutrition resources. I'd suggest that you go to Steve Pushak's website
and check out some of the many links he has there which cover the subject.
While many texts and sources might quote averages for the vaious elements
present in typical plant tissue, I have yet to see any claims (other than
this one) that there is ONE particular ratio or set of ratios that is
correct for ALL plants, or even all AQUATIC plants.
Plants absorb nutrients as and when they are available to them from their
environment. Many plants have the ability to absorb and concentrate more of
certain nutrients than they need for current use and to store this excess in
their tissues for use later, when the enviromental conditions might change.
An analysis of plant tissue will only reveal those elements which are
present in the sample, and is not necessarily a measure of the levels which
are required for optimal growth. It takes more than a simple chemical test
to determine the optimal level (and ratio) of nutrients required for plants
to grow to their full potential. As well, some plants can and will absorb
and retain elements which are not essential for growth - the presence and/or
levels of these elements in a tissue analysis is not indicative of a NEED
for this particular element, it is just a measure of what the plant absorbed
from the environment in which it was growing. And nobody, to the best of my
knowledge, has ever shown that ALL plants need or can use the SAME amount or
ratio of all the various essential elements.
If you look at the elemental analysis of a number of different trace element
mixes, you will not find exact agreement on any ONE set ratio of one element
to another. All trace element mixes are designed to supplement the nutrients
naturally present in the environment the plants are being grown in - these
environments vary drastically so no ONE mix could ever hope to be optimum in
As Greg Morin pointed out, various trace elements are used at different
rates and some remain bioavailable for shorter or longer periods of time
once introduced into an aquarium environment. Iron is probably the "trace
element" which is needed in the largest gross amount and it is also one of
the most transient in that it is readily oxidized and thus becomes both
unavailable to the plants and very difficult to detect with quick and dirty
Your desire for a simple solution is understandable, a lot of us might wish
that there was a "paint by numbers" approach which could work for all
situations, but unfortunately such an approach isn't likely to be found by
anyone any time soon.
Seachem's introduction of Flourish Iron was in recognition and response to
the fact that the typical planted aquarium needs more Iron than the other
various trace elements and the fact that Iron is much more transient in its
availability than the other trace elements. Trying to maintain adequate
levels of Iron using Flourish alone is, as Greg pointed out, likely to lead
to oversupply of the other trace elements and could result in some of them
building up to potentially toxic levels over time. Separating out the Iron
into a separate product is an elegant and economical solution to the
My own experience as well as a review of the many, many posts made to the
APD over the past few years regarding testing for Iron leads me to believe
that the use of indicator plants is a far more reliable method of determing
how much Iron your tank needs than any test kit can ever hope to be. You
need to start really looking at your tank, maybe taking notes and photos as
visual records over time and learn for yourself how your tank and your
plants react to the fertilizer inputs you introduce.
All the test kits in the world aren't going to ever replace the visual
feedback you get from actually looking at how your plants are growing.