On Tue, 23 Sep 2003 04:07:38 UTC, "Djay"
wrote:

A long time ago I read on one of the NG that someone put pieces of steel
wool in the substrate and thought the plants were thriving because of it.
Need a chemist to answer these burning questions....

Better, a biochemist or a plant physiologist.

as the iron oxidizes
in the water, does it become available to the plants?


I'm neither of the above, but here are some Iron Facts from a bio major
who stayed awake in chem:

Putting a nail in the water: forget it. Everyone knows that rust doesn't
dissolve readily in water, but iron (ferric) oxide (or rust) is really
_remarkably_ insoluble at any decent pH. If you run the standard
calculation that every chem student knows, you find that at pH 7.0 the
concentration of Fe+++ is a fraction of trillionth of a milligram per
liter. A good concentration is a tenth of a milligram per liter, so this
just really won't make it.

Turns out that the calculation is not really accurate, for a bunch of
reasons. According to
http://jchemed.chem.wisc.edu/Journal...abs1558_1.html
the real concentration is way up in the millionths of one milligram per
liter. Still not enough, though.

So much for chemistry and the nail in the water.

Burying iron in the substrate (as steel wool or whatever) just might work.
It will turn to rust, and plant roots have marvelous ways of extracting
that very insoluble iron from iron oxide. One method involves secreting
hydrogen ion, making the microscopic area around the root hair strongly
acidic. A bit of the Fe+++ goes into solution there, and the root absorbs
it (also reducing it to the ferrous state Fe++, which is not very relevant
here).

That's what lots of plants do in soil. Will your aquatic plants succeed
in doing the same? I don't know. Being a matter of biology, it can't be
answered from first principles.

You may want to experiment with this method. But before you do, remember
that the steel wool will turn into a mass of rust. When you uproot a
plant, which happens pretty often if you're maintaining a pretty tank, up
comes a lot of rust into the water, to settle down on the bottom and the
plants. You might not like that.


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