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Re: More Chemistry questions

On Sun, 21 Mar 1999, Dennis wrote:
> Now my other question.  I'm presently running a mixture of well
> water dKH 27 dGH 30 through a commercial water softener which
> is giving me water at dKH 3, and dGH 27.  My fish tanks now
> are a blend of this to give me about 14 dKH.  Within a week or 
> two I expect have a RO system on line also.

Hmm.  It looks like you may be getting your Gs and your Ks crossed up.
The softener that I *think* you're describing might drop the GH from 30 to
3, but it shouldn't change the alkalinity (KH) at all.  It should stay at 

> My questions are what does the commercial softener do to change
> the water chemistry.  Since it is using salt My suspicion is it is
> substituting Sodium and or Chlorine atoms to make the water appear
> softer.  But what chemical are left from these and can they be 
> harmful to fish and or plants?  

The system works by trading magnesium and calcium from the water supply
for sodium stored in an exchanger (usually a zeolite).  The trade is done
on an equal equivalents basis;  a milliequivalent/liter (20 mg/l) of
calcium is removed from the water and replaced with ("exchanged" for -
hence the names "exchanger" and "cation exchange") a milliequivalent/liter
of sodium (23 mg/l).  The general hardness - which is created by calcium
and magnesium - drops and the total dissolved solids content increases.  
The increase in dissolved solids is small if the hardness is mostly caused
by calcium, but its fairly large if the hardness is caused by magnesium.

When the exchanger is just about filled with calcium, then the system
makes a brine from salt (NaCl) and flushes that through the exchanger.
That reverses the softening process; it knocks the calcium and magnesium
off the exchanger and replaces it with sodium.  The chloride from the salt
is washed on down your drains along with the calcium and magnesium.  You
should never see an increase in chloride due to the softener, but I think
it can happen anyway if the brine isn't completely flushed out of the

These systems remove magnesium in preference to calcium, so the softened
water can be pretty much devoid of magnesium, low in calcium and will have
a lot of sodium in it.  That may cause your plants some problems.

> Also when I install the RO system would I be better off hooking it up 
> to the pre softened water or to the raw well water?

I think you need to ask the manufacturer that question.

> My general idea after
> getting it is to use a mixture of about 1 part raw well water to 5 parts
> RO water hopefully will bring my water down to about 6 to 7.5 dKH.
> However people also tell me the pH will probably not change.  Will the
> addition of CO2 bring my water down from the present 8.4 pH and keep
> the CO2 ration properly in line with the prior quoted formula?

CO2 should drop the pH, and unless your well water has some unusual buffer
in it it should be consistent with the quoted formulas.

Roger Miller