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Re: Softened Water

First a couple of previous posts:

>> Date: Sun, 21 Sep 1997 23:08:35 -0600
>> From: Samir Makar <smakar at cableregina_com>
>> Due to the proximity of my holding tank, I am using softened water.  I pleased with
>> the results, especially since experimenting with DIY CO2 and PMDD.  Am I
>> lucky, or just not realizing my full potential.  Does anyone know how
>> much Sodium is being put into the water.
>Date: Mon, 22 Sep 1997 11:12:12 -0500 (EST)
>From: "Roger S. Miller" <rgrmill at rt66_com>
>Subject: Re: Aquatic Plants Digest V2 #969
>
>That depends on how hard your water is and how well the softener is
>working, either of which can change from time to time.  But there is a
>way.
>
>Measure the hardness in unsoftened water and in the softened water, and
>subtract to find out how much hardness has been removed.  Then:
>
>if you measure hardness as ppm CaCO3
>
>sodium increase (mg/l) = 0.46*hardness decrease (ppm CaCO3)
>
> or
>
>sodium increase (mg/l) = 8.2*hardness decrease (degrees)
>
>The uncertainty in this calculation is _big_ because you get it by taking
>the difference between two hardness calculations with very tall error
>bars.
>
>RgrMill
 
Another Post ...........................
 
>Date: Mon, 22 Sep 97 15:33:39 cst
>From: mark.fisher at tpwd_state.tx.us
>Subject: Re: Softened Water
>
>     >As I understand it, a softener exchanges Ca and Mg ions for Na ions,
>     >so the amount of Na added is equal to the amount of Ca and Mg that
>     >you had to begin with.
>
>     Actually, as Ca and Mg are divalent cations (they have a +2 charge),
>     two monovalent Na cations (they have a +1 charge) are needed for
>     exchange.  Thus, for every Ca or Mg ion removed, two Na ions are
>     added.
>
>     By weight, however, if a softener removes 100 ppm Mg, then it must
>     release 189.2 ppm Na (Mg has a higher atomic weight than Na).  Removal
>     of 100 ppm Ca releases 114.7 ppm Na.
>
>     Kind regards,
>
>     Mark
 
 
I'd like to add my 2 cents worth in to this discussion.

Watersoftners use Zeolite to remove "hard water" minerals from your household
water.  The basic formula for conversion is given (ASCII art) by:
 
      2NaSiAlSO4      +      Ca++      ->      Ca(AlSi04)2      +      2Na+
 
     (Sodium Aluminum       (Calcium            (Calcium Aluminum       ( Sodium
       Silicate)              ion)               Silicate)                ion)
 
      (Magnesium ion (Mg++) can be substituted for the calcium ion.)
 
This equation says (do to charge conservation) that two sodium ions are needed to
replace one calcium ion.
 
Watersoftners do a good job of removing most of the calcium and magnesium. When
I measure the hardness of softened water, it is below 0.5 degrees GH. (Limited by
my test kit.)
 
By knowing the atomic weights of calcium and sodium (Ca => 40 and Na => 23),
and using Neil Frank's article "Determining the Concentrations of Chemicals Added to
the Aquarium" TAG Vol.10 No. 2, I know how to convert from degrees calcium hardness(GH)
to ppm sodium concentration. So, using the assumption that each calcium atom
is replaced by two sodium atoms:
 
1 degree GH = 17.9 ppm Ca = 2 x 23/40 x 17.9  = 20.6 ppm Na
 
 
From which we can produce the following little reference table:
 
Estimated Sodium in softened water     ( 1ppm = 1mg/liter)
----------------------------------
   |Before GH  |Converted Na |
   | (degrees) | (mg/liter)  |
   |-----------| ------------|
   |     1     |     20.6    |
   |     2     |     41      |
   |     5     |    103      |
   |     10    |    206      |
   |     15    |    309      |
   |     20    |    412      |
   |     25    |    515      |
   |     30    |    618      |
   ---------------------------

Another thing to remember, a watersoftner waste salt when it recharges the Zeolite.
Thus, one may expect to get even higher levels of sodium just after the recharge.
 
Let's get a feel for what these numbers mean.
 
Water hardness follows these guidelines:
 
      0 -  4 dH,    0 -   70 ppm : very soft
      4 -  8 dH,   70 -  140 ppm : soft
      8 - 12 dH,  140 -  210 ppm : medium hard
     12 - 18 dH,  210 -  320 ppm : fairly hard
     18 - 30 dH,  320 -  530 ppm : hard
      above                      : very hard
 
The water in the Allentown area is around 12 degrees, which means
I'd estimate my water sodium concentration to be about 250 mg/liter.
 
A lot of us use baking soda to raise the KH in RO water to about 4 degrees KH.
(Remember GH and KH are not the same thing.)
 
 4 degrees KH = 4 x 17.9ppm HCO3 = 71.6ppm HCO3
 
In baking soda, 73% of the weight is from HCO3 and 27% is Na.
 
so 4 degrees KH => 27/73 x 71.6 ppm = 26.5 ppm Na
 
For most fish and plants, I would not worry too much about 26.5 ppm Na.
For humans, consuming less than 2400mg per day is recommended. (U.S. Dept.
of Agriculture?)
 
Maybe someone on the list can comment about which fish and plants are sensitive
to sodium and at what levels.
 
---------------
 
Ron Wozniak  Allentown PA, USA
rjwozniak at lucent_com