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Re: NFC: aquarium basics site

On Wed, 17 Nov 1999, Sajjad Lateef wrote:

> 	What is a TDS meter? (perhaps Total Dissolved Solids aka
> hardness?). I am not quite sure. 
TDS is total dissolved solids.  TDS does not mean hardness, it means TDS.
In general, hardness is only a measure of Calcium and Magnesium salts in a
solution, while TDS takes EVERYTHING into account, such as tannic acid and
so forth.

> 	Are pH and hardness related? I have been under the impression that
> lower pH and lower hardness were synonymous. 
pH and Hardness are not in any real way related.  Nor, of course, are
lower pH and hardness.  Water that is less hard is generally more acidic,
and conversely, water that is more hard is generally less acidic.  The
reason for this is that the hard water may contain compounds that include
the OH- group, or, much more likely: buffering.  Buffering is a relatively
complex topic, but basically what it means is the ability to resist a
change in pH.  So, while increasing the acid concentration in pure water
ten times will result in pH being decreased -1, in a good buffer, it may
have no effect.  (Though, of course, pH will still drop for a short
period.  This is why it is impossible to keep fish requiring acidic water
in hard water.... The water naturally bounces back a few hours to a few
days after the acid is added to reduce the pH.  This is quite stressful...
especially since the pH scale is logarithmic and we tend to attemmpt
changes by full points or more on it.  A pH of six is ten times as acidic
as 7, and one hundred times as acidic as 8.  So, adding enough acid to
drop the pH in your tank from 8 to 6 is quite stressful, as is the
bounce-back.  Enough rambling from me in parenthesis)