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Re: Iron - Chelated - Ferrous - Ferric - lost and found
- To: Aquatic-Plants at actwin_com
- Subject: Re: Iron - Chelated - Ferrous - Ferric - lost and found
- From: Roger Miller <roger at spinn_net>
- Date: Wed, 2 Apr 2003 08:01:54 -0700
- In-reply-to: <200304021205.h32C59V4025464 at otter_actwin.com>
- References: <200304021205.h32C59V4025464 at otter_actwin.com>
On Wednesday 02 April 2003 05:05, Scott Hieber wrote:
> So the iron can be gotten by the plants (eventually),
> sooner or later, regardless of whether it's about the tank
> as chelated, ferrous, or ferric? If you dose it, they can
> use it even if your (initial or edta) chelators are being
> photoreduced and you're photoreducing the "free" iron,
Yes, but with complications. Some of the mechanisms that plants can use to
get different forms of iron are not triggered until *after* the plant is
already stressed for iron -- not till after the plant is already deficient in
iron. Some of the mechanisms plants can use are also very expensive to the
plant in terms of the amount of chemical energy and fixed carbon they
require. It seems like that expense must result in a reduction in growth.
Further, different plants vary considerably in their ability to get iron when
it is in low supply, so some plants can be failing with iron deficiency while
other plants in the same aquarium show no deficiency problems.
Plants need something like 1x10-9 molar of biologically available iron.
That's about 0.06 parts per *billion*. I don't think even good test kits
will measure concentrations that low. Concentrations of chelated iron are
generally not significant. That's because the chelated iron isn't
biologically available until after the chelate complex breaks down. Test kit
results that include chelated iron are only useful as a general indicator of
the size of the dissolved iron "pool" that might be available to plants. The
amount of iron you need to register on the test kit varies a lot depending on
the exact nature of the kit, the kind of chelating ligand used and other
variables that I don't know or don't understand.
For iron, I think the best approach is to throw away the test kits and just
make sure that the plants have access to multiple iron sources -- in soil
humus, substrate solids and low levels dissolved in the water.
> Scott H.