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Re: fluoride "problem"

On Tue, 27 Jun 2000, Neil Travis wrote:

> I think you had better re examine your chemistry.
> In Melb if we have any clay deposits in the water it completely chelates the
> fluoride.

"Chelate" is the wrong word.  Maybe "bind"?

Fluoride substitutes for small amounts of hydroxide in some minerals.
Clay minerals contain hydroxides in their "octahedral layer" so I imagine
that fluoride may fit in there, too.  I think it's more likely that the
flouride would substitute for hydroxides in precipitating iron or
manganese hydroxides.  Once precipitated it would be there pretty much

> Say you have a 10% evaporation rate then you have 100% of the fluoride in
> 90% of the water then you remove another 15% of total tank capacity and
> replace it with 25% of tank capacity to fill it then you have 115% of
> original Fluoride concentration and so on with every water change. Simple
> mathematics.

For the most part, I expect that fluoride in the water will be pretty
unreactive and will just stay in the water until it encounters something
with an unusual affinity for it.  But given enough time some precipitation
will occur, and that may be sufficient to offset the evaporative buildup
of fluoride in the water.

> on distilled water I did not advocate using plain distilled but using it as
> a starting point. I add salts to mine but at least I am sure it is fluoride
> free as I have had many experiences with Fluoride egg hardening and after a
> lot of experimentation and consultation with Melbourne water got it right.
> Hardening of eggs is fairly obvious when you see a fish in an egg trying to
> get out but can't and eventually dies.

I checked and I have been completely unable to find evidence for fluoride
affecting aquatic life.  There are no water quality standards for that
purpose (the standards are for human health and aesthetics) and I've found
no discussions of any other effects.  If there is a relationship between
fluoride and low hatch success then the environmental regulators -- who
tend to be sensitive to that sort of thing -- would *definitely* be paying

More likely there *is* no effect on fish eggs (despite the unscientific
observation) and certainly no effect of fluoride on the health of
anybody's bettas.

Then Bob Dixon wrote:

> I once asked a chemist friend about something to remove calcium and magnesium
> from the water and precipitate it.  HFl came up as an option, but he assured
> me that the flouride ions were reactive enough that my tanks would suffer
> from its ability to dissolve glass.  Glass is also extremely "stable" but not
> immune to flourides strong reagent ability.  So it would seem to me that
> silicates in any form would not be safe from being knocked loose and replaced
> by Fl ions.

Hydrofluoric acid does etch glass and it does dissolve silicate minerals,
but really Bob, there's a lot of thing that will happen in a concentrated
solution that will never happen in a dilute solution like 1 ppm of
fluoride in tap water.  For example, concentrated sulfuric acid and nitric
acid together make an extremely corrosive, oxidizing acid called aqua
regia that also dissolves many minerals -- even some that hydrofluoric
won't touch.  We pretty much all have sulfate and nitrate in our tanks --
and at levels greater than 1 ppm -- yet we aren't sweating their combined
effects on glass, fish eggs, fish or whatever.  Those effects don't
happen in dilute solution.

If we have so much time on our hands that we can afford to worry about the
possible effects of fluoride then maybe our time would be better spent
worrying about the effects of chloroform and trihalomethanes (carcinogens)
resulting from chlorination of tap water, or about the toxic copper and
lead introduced to some tap water at microgram/liter levels just from
flowing through the pipes in your house.

Also, this thread is completely unrelated to growing aquatic plants.

Roger Miller