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Re: NFC: aquarium basics site

Sajjad Lateef wrote:
> On Wed, 17 Nov 1999, Wright Huntley wrote:
> > could use it a lot. I actually use it about (maybe) once a month. OTOH, my
> > tds meter gets used several times a week, as osmotic shock is truly harmful
> > to fish (particularly if tds change is downward by a serious amount). KH/GH
> > titration test kits are too slow and cumbersome to be that useful, IMHO.
>         What is a TDS meter? (perhaps Total Dissolved Solids aka
> hardness?). I am not quite sure.

In truth, it is a conductivity meter, but calibrated in ppm (parts per
million) of tds (total dissolved solids) as the two are pretty well
correlated in normal water.

>         Are pH and hardness related? I have been under the impression that
> lower pH and lower hardness were synonymous.

No relationship whatsoever. 

Most US water has some exposure to ancient seabeds, and CaCO3, so the
combination tends to be hard, alkaline and have a high pH (not the same
thing as alkalinity, BTW). The carbonate/bicarbonate combination buffers the
water to that higher pH *and* gives it the alkalinity (ability to absorb
acid without pH drop). The hardness (Ca and Mg ions) just happens to be
along for the ride. 

Soft water OTOH is usually essentially unbuffered and can have almost *any*
pH. The atmospheric CO2 tends to push distilled or deionized water down from
neutral (7) toward 6. Organic acids can lower it further.

That apparent correlation between pH and hardness is what most folks
observe. It is actually just a coincidence.

My RO (reverse osmosis) water, at 10ppm tds, initially is about pH=8. On
standing, that drops a lot, and with some peat, I can easily push it down to
pH=4. My 270ppm tap water, OTOH, is about 200ppm hardness (CaCO3 equivalent)
so it is difficult to get it down even to neutral without creating a horrid
chemical soup.


Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

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