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Re: Rusted Rock

Beverly Wladyka wrote:
> A recent trip to a local quarry lead to us to bringing home some of the
> smooth black river rock (our guess is that it's basalt) we'd hoped we'd
> find (plus, in the small quantities we need for an aquarium, we got the
> stuff free).  The only problem with some of the rock is that it is
> stained, in some places, with rust.
> My plan is to soak these rocks for a week then test the water for iron
> to determine iron content, but first have a few questions that I hope
> the learned folks on the list can answer.  Is the rust going to be a
> problem for the fish?  Will the rust and the iron from which the rust
> comes be of any use to the plants?  Should rusted rock be used in an
> aquarium at all?

Rust of itself is not a problem to fish or plants. Rest assured that its
not going to have much effect upon the concentration of Fe in your
aquarium water nor will it add enough to make any difference to the
plants. There are basically two ways of supplying iron to plants:

1) in solution as chelated iron
2) in the substrate in the form of very fine textured clay (which
normally contains iron oxides)

There are many cheap and effective products and DIYS chelated trace
element powders so that it is quite easy to use method 1) to supplement
a high light, high growth tank where you are supplying enough other
nutrients to require extra iron. If you use a lower light level (which
is often MUCH easier to manage for beginners) and/or you grow plants
which are slow growing root feeders (e.g. Crypts), then you will
probably be able to get all the iron needed from the substrate. Combine
some peat with a clay (or clay-soil) substrate, and you should even get
enough Fe in solution to keep floating plants green and growing rapidly.
In my experience, not all soils are equally good at providing iron but
probably benefit greatly from addition of a little peat and/or clay.
Peat (or humus) provides natural organic chelators (humins) and clay
provides the very fine texture particles necessary for intimate root
contact and sufficient surface area for good chemical interaction.

Your third question is the most interesting. A rusting rock is evidence
of a rock which may be crumbling and there is always the chance of other
toxic minerals (heavy metals) being present. Its difficult to give
categorical advice about the suitability of rocks. Igneous rock is
possibly the most stable. I'd beware of colored rocks especially green
color as this might indicate copper deposits. Copper is a no-no. Someone
more qualified than I might comment on geology and rocks.

Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!