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listhub at libros_andante.mn.org (Anonymous?)
> Since no one replied I will take a shot.
> On 08-Sep-00 Ryan Deal wrote:
> > Hello,
> > I was wondering if there is any "link" between dH and TDS.
> Not much.
> dH or GH is total hardness. It is measure of combined carbonates, sufides,
> sulfates, silicates, etc.
Not quite. It is a measure of the divalent metal ions, like Ca and Mg.
> TDS is a measure of ion conductivity.
> Now the ions that will contribute to GH will also contribute to TDS, but the
> recipricol is not the case. Things like NaCl or KCl will contribute greatly to
> the TDS but very little if any to the GH. So your question:
> >For instance,
> > if the water had a dH range of 7.0-9.0, what would that be equal to in TDS
> > terms (if they are related at all?).
> can not really have an accurate answer. If the mono ion concentration is
> constant then the TDS might be an indicator of GH but you would need to
> calibrate it for your water. In fact, I really do not know why people use TDS
> with Killies. It is used a lot with Discus and this is becuase at the dH (0 -1)
> that people use to raise Discus, if the TDS is low the slime coat on the Discus
> is inhibited. This makes successful fry rearing very hard.
> I know of no corresponding situation with Killies.
I must disagree, here. Killies are dependent on osmotic pressure to regulate
the amount and salinity of bodily fluids, just like any other fresh-water
fish. Conductivity, which we measure as tds, is very closely linked to the
osmotic pressure across the cell membranes in such fish. Sudden changes in
it are what gave rise to all the old "pH shock" myths.
The jury is still out on the effect of the hardness ions (divalent metals
like Ca, Mg, Fe, etc.) on rain-forest killifish egg development. There is
little dispute of the fact that suddenly dunking a killy from high tds water
into RO or DI will damage gills and usually kill it dead.
The tendency of discus breeders to use that very low GH water may have made
them more aware of this problem earlier, but the situation is very similar
for killies. In general, tds is many times as critical for killy health as
the Ca, Mg, etc., concentrations. The rest of your explanation was right on.
tds and GH are only related by a loose coincidence, and the value of one is
a poor predictor of the other.
Wright Huntley, Fremont CA, USA, 510 494-8679 huntleyone at home dot com
"People constantly speak of 'the government' doing this or that, as they
might speak of God doing it. But the government is really nothing but a
group of men, and usually they are very inferior men." --H. L. Mencken
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