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Re: rocks in the aquarium

Daphne Freeman wrote:

> The "iron oxide?" I was referring to in my slate will dissolve in water if
> you bump the slowly increasing deposits they form underwater.  It is almost
> powdery out of the water and readily makes a mess and dissolves if you run
> your finger across it in the tank.

To be strictly correct we would be talking about iron hydroxides or
oxyhydroxides, not actual iron oxide.  That is probably a minor point to
most people.

If it does actually dissolve then it isn't an iron deposit.  On the
other hand, it's possible but unlikely that any kind of deposit that
formed underwater would redissolve into the water just from being
disturbed.  Are you sure it isn't simply dispersing, rather than

Oxidation of iron minerals under aquarium conditions is probably
performed by specialized bacteria.  Collectively, these bacteria are
just called "iron bacteria"; there are quite a few unrelated strains of
bacteria that do the same thing.  The bacteria form a colony near the
source of the iron and the colony becomes coated with the iron deposits
that they form.

We typically associate rust-red color with iron deposits, but fresh
deposits may also be brown, yellow or orange.  The fresh deposits would
also be a low-density mixture of biological material and iron deposits. 
It would be loose -- maybe even slimey -- under water and should dry to
a flaky or powdery consistency.  The deposits probably would harden over

> Even though it dissolves would it still be stable such that I shouldn't
> worry about it affecting the plants?

If it actually redissolves rather than dispersing then I can't answer
that question, because then I don't know what it is.

Roger Miller