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Re: dH/TDS

Those turned off by Physical Chemistry of water solutions, hit the delete
button.

On 11-Sep-00 Wright Huntley wrote:
> 
> 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.
> 

All ions contribute to TDS.  Ca++ Mg++ Fe++ contribute the same as Na+ or K+. 
In fact the movement of an electron through a solution of any substance is
dependent on the facility of the electron to enter the outer orbital shell of
whatever positive ion is available, often referred to as "solution resistance"

TDS is a measure of this conductivity.

Osmotic pressure is the difference between ion concentration on one side of a
membrane (or piece of dialysis tubing) and the other.

TDS is no better measure of that difference then something which actually
measures ion concentration in a different manner.  In fact, it is not as good. 
If you take a solution of Fe++ that has a relatively low delta between the
outer orbitals that the electron will enter and leave (low solution resistance),
this solution will have a very high TDS (conductivity) for a very low ion
concentration (osmotic pressure).  If you use Na+, high resistance to electron
flow, to achieve the same TDS as the Fe++ solution you must have a higher
concentration of Na+ ions resulting in a higher osmotic pressure.

Your statement that osmotic pressure is is necessary to regulate body fluid
levels is important is cure.  Using a TDS meter vs a solid measurement of dH
(GH) is what I question.  I have been spawning discus for 20 years and never
gave a #$@% about micro-Siemens.  I know what my GH, KH, and pH are. I don't
worry about conductivity.

Is measuring conductivity a good thing, yes.  But IMHO not as important (or as
cheap to measure) as the other three.

Peace
john
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E-Mail: listhub at libros_andante.mn.org
Date: 11-Sep-00
Time: 18:07:33

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