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> If you
>see a response to increasing iron content from e.g. 0.5 to 1 ppm there are
>a few things I can think of that could explain the response:
>1. Only a very small part (perhaps 1/1000th) of the iron you are
>measuring is available to plants.
I use lots of TMG as a source since it is well used and observed by such
folks as Claus/Neil/Karen/Kasselmann etc and they know what deficiencies
look like. I figured awhile back that it would allow me to have "some degree
of standardization" comparing notes with other plant folks. There's not
much "Free iron" by any means but using TMG and using a pricey Hach test
Kit, I think the data plus the combined observations of others lends itself
the support for this. I have a hard time telling the big guy from Tropica,
the largest aquarium plant producer, he's nuts :) I'll take his word on it
>2. The observed change is not in response to iron, but in response to
>some trace nutrient that accompanies the iron, perhaps even as a
If this were the case, with Hach ""water testing"" equipment that is
designed specifically for water testing, I think basic elemental
interferences would be accounted fer! Or I would hope so anyhow. Not that
even some very reliable test kits are that great for differing types of
bound Fe's and Free iron. Some are wrong likely but how much of a precise
reading do we really need?
Plenty of folks maintain a "range" of nutrients with the cheap lowly types
of kits with amazing results. Lucky 100% of the time for years? Doubtful.
Well, each case is different but how do we standardize things? A special kit
for a special type of fertilizer? A different set up for Flourite or
laterite based tanks? Different levels? How much real concrete data can be
collected by the average hobbyist to get a decent reading? I found that a
presence-absence test worked fine using a cheap test kit(Sera) to keep an
eye on the tank also. As you say, the plants don't need much.
>3. The test kit it wrong.
>The third option here isn't very interesting, so let's just assume that
>your test kit is right.
I wouldn't bet on it. See above. Need good water analyzer but a small amount
is all that is needed and this "range" doesn't have to be that accurate but
within a parameter. I'm not sending a satellite to Mars:) So the super duper
test kit won't be all that informative from a pactical standpoint.
>If either of the first two cases is correct then we have a problem. In
>the first case, any small variation in the biological availability of the
>iron will create a huge difference in your plants' response to iron
>fertilizer. I believe that the availability is going to vary a lot with
>factors like the kind of chelate, the temperature, pH, type of substrate
>and age of substrate. In the second case, the response you observe may not
>be seen at all by someone who tries to reproduce your results with a
>different iron fertilizer.
I certainly agree. Substrate fertilizers when added can allow almost no Fe
in the water column and great plant growth. This is a very effective method
that I used inadvertantly (I had idea why at the time) for a few years and
still do on a tank or two. I am not certain about the Binders attached to
them and the ability of each species of plant or specific sets of iron
seeking enzymes to break the bonds of each type to get the iron. But the Fe
is not "Free" once "inside" the plant either. Something carries it around to
be used at specific site. Perhaps a specific binder/chelator that the plants
use themselves could be made stable to hold the Fe in solution until the
plant could use it. It would be neat if the plants could use this specific
form of iron much easier than algae which may/might have a differing
chelator added to algae's bound Fe. That would be good stuff, eh?
>Please keep in mind that your results and the results of others are going
>to depend *a lot* on the fertilizer you use and the conditions in your
>tank. Fluorish Iron, for instance, provides iron as ferrous gluconate;
>ferrous iron is what plants actually use. Many other iron-containing
>fertilizers provide ferric chelates, like iron-EDTA (e.g. Tetra
>FloraPride) and iron-DTPA (Tropica Master Grow, I think). In those cases,
>the plants have to reduce the iron to ferrous iron and break the bond
>to the chelate before they can use the iron.
>At a minimum, a recommended iron level should be accompanied with
>information about the fertilizer that's used as a source and preferably
>there should also be some information about the substrate used in the tank.
Yes, true -see above. I agree with this last point in paticular as Roger
>Short answer: Iron is a trace nutrient; plants need damned little of it.
Also very true. Perhaps a super test kit and all the testing will not make
up for the discerning watchful eye of the aquarist?