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Re: iron

Roger wrote:
> One simple conclusion seems unavoidable; the plants are *not* using the
> chelated iron that we diligently add and carefully measure.  Rather,
> they are using the much lower levels of ionic iron that are released as
> the chelate breaks down.

I think you got it. Or they use the Fe3+ when they need it and convert it
themselves once they pull it in. Some let the bacteria do the work or the
acidic sub's.
It takes less energy to use the Fe2+ but it IS a trace element and does not
require a huge energy expenditure relative to the whole plant. Iron doesn't
evaporate either. I did not add any iron to the gravel of a number of tanks.
They did quite well. No laterite etc. Snail poop and traces add to the water

>  Plants probably won't use the chelated iron
> directly unless they are already iron-stressed, which appears as a
> visible iron deficiency.

This could be plant species specific?

> Some of us avoid the visible symptoms of iron
> deficiency by adding very high concentrations of chelated iron to the
> water column.  Ionic iron is only briefly available as the chelate
> breaks down, and keeping high levels of chelated iron makes sure that
> the ionic iron is always sufficient to meet the plants' needs.

Perhaps but the plants also get dosed 2-3 time a week so their Fe+2 needs
are being met based on the 20000 times or whatever excess we add.
> High iron levels could cause a number of different problems.  The main
> problem is just that you apply way more fertilizer than your plants
> actually use.  Also, many of us add iron in a trace mix and use iron
> measurements as an indicator for the adequacy of trace element
> concentrations.  It is very possible that as iron levels are pushed
> higher and higher that some other trace element in the mix will reach
> toxic levels.  Conceivably any of copper, zinc or boron (just to name
> three) could reach concentrations where plant growth is inhibited and/or
> invertebrates or fry are damaged.

Water change. Unless you get precipitates, copper etc or go plum wild and
overdose the heck out it. You types know who you are:) One guy added PO4
instead of KNO3 at 1/2 teaspoon levels instead of 1/2gram levels....
If I say 1.0ppm or so someone will add over 2ppm etc. More is better.
That's simply not true and will kill fish and not help the plants anymore.
At a certain point you simply just waste your fertilizers and traces.
There's a range that effective. More is wasteful and can cause problems, too
little stunts plants.

> Complicating matters even further, the level of chelated iron that's
> necessary to provide the desired concentration of ionic iron is going to
> depend on a number of poorly constrained variables.  Commercial iron
> chelate mixes use at least three different chelating agents (EDTA, DTPA
> and gluconate), all with different decomposition rates.  The
> decomposition rate of the chelate (and hence the supply of ionic iron)
> also depends on light intensity, light quality, temperature, and
> probably on bacterial activity.  Further, some aquarists keep substrate
> conditions (generally, acidic) that might make it unnecessary to *ever*
> add iron.

Well not in higher lighted tanks. I've tried this now a few times. It does
depend on plant species to some degree. Lower lighted tanks in the 2 watt
range certainly I'd say yes to this. Maybe 3 watt a gallon. But the higher
lighted tanks need both unfortunately. I've tried to get around it but I
just don't think it's possible. To have good growth at higher lighting
levels, we need both sources(gravel and water column). But I get better
growth even on the lower lighting tanks with good high CO2 and nutrients but
less than the higher light tanks on the traces.
> If you need to add iron at levels that are pushing 20000 times the
> essential concentration then maybe it's time to look for be a better way
> to fertilize your tank.

Perhaps, but it works. Why? Why not do this also?
Tom Barr 
> Roger Miller