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Re: musings on water changes



At significant risk of frustrating George even more...

Roger Hawthorne wrote:
> Wright:
> 
> Guess I was thinking  the buildup of minerals that could  
> prove harmful would be quicker in hard water, and that
> what makes water hard is as important as how hard. 

Only three things commonly make water hard: Calcium, Magnesium and Iron 
ions. Since Iron is usually just a trace, Ca and Mg are the divalent 
ions that make suds "hard" to generate with soap -- the definition of 
water hardness. They are usually present in some 80:20 or 70:30 ratio 
that is pretty much the same most places.

If you are adding water from the same source, the minerals cannot build 
up, much, even with some evaporation. The water change will always tend 
to push their concentrations back down to the average level, which will 
be barely above the amount in the change water. [Did you notice my 
clever avoidance of the use of "equilibrium" in that statement? :-)]

"Carbonate Hardness" is just alkalinity, as we measure it (KH kits), and 
has nothing to do with real hardness. It buffers pH high and that can 
make ammonium turn to ammonia and do gill damage if too much ammonia is 
present. The term apparently sneaked into the aquatic English literature 
via some chemically-ignorant translations from German about 50-60 years 
ago. Like pH shock, it seems to have an endless and misleading life.


> I
> have noticed tanic acid from 'Malaysain Wood' affect the
> growth of Africans les than acid from breakdown of
> ammonia. 

That may be because ammonia itself is the culprit in a lot of stunting, 
but the acid produced by nitrate buildup is not felt by the fish and 
does nothing to their growth at levels below about 300 ppm. There's a 
whole lot of mythology in this area.

Acidity has little effect on fish health and growth.

Bottom line: Change water.


> I am simple minded. My tongue can tell the  
> difference between coke, coffee, and tea. My test kit
> cannot. There are other things that make water acid
> and/or hard that I don't want to be able to tell by taste.

:-) Yeah. We sure agree on that!

> What causes the TDS seems to me to be as important
> as what the TDS is. 

The real importance of tds is its close relationship to osmosis and the 
bad effect on fish if they are subject to abrupt changes in osmotic 
pressure (this was once the old pH mythology, that was discredited by 
Scheel and others many years ago -- still shows up in books, anyway). It 
matters little if the tds is in dead soft water (e.g., a lot of salt) or 
very hard water (lots of CaCO3 equiv.), if you suddenly drop the tds it 
can damage gills and skin and cause all kinds of disease outbreaks, even 
if it does not kill the fish at once. Osmosis seems amazingly uncaring 
about *what* the particular ions are, just how much pressure is caused 
by the dissolved stuff.

Other tank chemistry and biological processes may be very dependent on 
the exact makeup of the dissolved solids. That is taking us where George 
was getting frustrated, so I'll just leave it there. :-)

Avoid tds shock by doing smaller changes more often.

Wright

PS. Simple version for George: "Water changes are good." :-)

-- 
"Deport all the product-liability lawyers to Iraq;"
                                 -- Dave Barry --
       [Best suggestion of 2002, by far...]
              <www.sfbaka.net>


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