Re: Water Chemistry

[IDMiamiBob@aol.com]

Edison writes

>I would like to know if water that is acidic to be also hard, could this be
>possible?  Also, could water that is soft be also alkaline?  

>When we say soft water what is the calcium content mg/litter?  How about
>conductivity,  what is the significant of this to fish keeping?

Big John writes:

> I dont know about water that is acidic and hard but i do know that you
>  can have alkaline soft water.   A friend has some , pH of 8.0 and only
>  60 ppm hardness.

Be careful when using the term "alkaline".  Alkiline water is water which 
resists a drop in pH.  Water with a high pH is actually refered to as "base" 
water.

Water can be high in dissolved solids with a +2 ionic charge, and therefore 
"hard" while lacking any alkalinity at all.  It can be acidic and still have 
lots of dissolved calcium and magnesium.  It can also be "base" and have no 
hardness at all.  If you started with distilled water and added sodium 
hydroxide, it would have a high pH.  If you start with distilled water and 
added sodium bicarbonate, it would have a high alkalinity, and would drift in 
the direction of a high pH. 
   If you start with distilled water and added calcium chloride, or magnesium 
chloride, you would have "hard" water.  If you added hydrochloric acid to 
that, it would be hard water that is acidic and somewhat saline (salty).  Add 
nitric acid instead, and it would be hard with a lot of nitrate.

In nature, bodies of water tend to start with rain water, which is 
essentially distilled, except for some dust and pollutants it picks up from 
the atmosphere.  It will also have some carbonic acid, which is formed when 
water mixes with carbon dioxide from the atmosphere.  As that rainwater 
passes along streambeds, it dissolves various minerals.  Plants that live in 
the water or along the shore add their own chemicals, which tend to 
neutralize the dissolved solids from rocks and stones further upstream.  Each 
mile of stream causes modifications to the actual chemical makeup of the 
water.  

Yes, you can have "soft, base" water.  And you can have "hard, acid" water.  
Most often, when stream water is absorbing calcium and magnesium, it also 
absorbs some carbonate.   This is not always the case, however.  And 
sometimes, either the calcium and magnesium, or the carbonate, gets 
neutralized and taken out by other things in the water.

As for what is considered "soft", that may depend on who you talk to.  I 
consider hardness of 60ppm or less to be soft.  Others say anything under 100 
ppm is soft.  I think the safest definition involves the the idea that it is 
all relative.

Conductivity is an indirect way of measuring total dissolved solids.  Harder 
water has a higher conductivity than softer water.  For fishkeeping, this is 
significant in the same way that hardness is.  Soft water fish live in water 
with low conductivity, and usually the lower the better.  Hard water fish are 
genetically aclimated to high conductivity. 

 The real issues around hardness and conductivity have to do with how the 
species has adapted to maintaining the proper water content within its cells 
relative to the water around it.  Water tends to pass through cell walls from 
the areas of low dissolved solids to areas of high dissolved solids.  This is 
about getting everything distributed evenly, which nature seems to insist on. 
 Saltwater fish must constantly get more water into their body, while 
freshwater fish must pump water out.

I hope this helps without getting too technical.

Bob Dixon


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