Well, it's been a few years since I posted to this group, but I'll give
it a go. I have degrees in pharmacy & biochemistry, but I'm not going
to draw any fancy equilibrium reactions or anything too over the top.
And note that my hero, Craig Bingman, was posting about this 12 years
ago on USENET - so credit where credit is due...

Basically, when you add a salt (say, Calcium Chloride - CaCl2) to water
(even sea water) it breaks up (dissociates) into IONS. They are
electrically charged (+ or -) versions of atoms. So in our example, we
have Calcium (Ca++) and chloride (Cl-) ions floating around now in
solution. Ions are not the same thing as their elemental versions -
which is a good thing - so this is why you do not get the chloride ion
"gassing off" into the atmosphere as chlorine gas and conveniently
leaving you the calcium.

Same with ordinary table salt; dissolve some in water, and you do not
get elemental sodium or gaseous chlorine (both are nasty pieces of work
in their elemental state, BTW)

Anyway, so, you dutifully add calcium chloride to boost your calcium
levels - using the logic, as your correctly pointed out out, that it is
a more concentrated way to supplement calcium. What are the long-term
consequences of this? Well, our systems use calcium up - both as
calcium carbonate precipitation, and in calcifying organisms. If you
only supply your calcium as CaCl2, you are setting yourself up for an
ionic imbalance. How this happens is that the leftover chloride ion
wants (has to, actually) have an oppositly charged partner - which it
gets in the form of a H+ ion. Now you have HCl - aka hydrochloric acid.

This is why people try adding the sodium bicarbonate to counteract this
and to replace "alkalinity"

So the Sodium (Na+) counters the Chloride (Cl-) which if you recall is
simple table salt... now you might think all is well - sea water is
mostly "salt" right... but in both cases, the Sodium, and the Chloride
ion concentration are rising in compared to / at the expense of the
other *important* ions in sea water, like strontium, magnesium, etc.
This is your ionic imbalance. Over time, your salinity may well rise,
but what you have in your tank is getting farther & farther away from
Natural Sea Water (NSW) concentrations of all the many, many elements
besides just Na+ & Cl-. In other words, you do not have a natural sea
water residual. You can try and correct this with water changes, but
forget about little ones (like 10% a month) doing the trick.

You could try and make up a fancy alkalinity buffer (sodium bicarb +
sodium carbonate + other chemicals, but this gets tricky & involves a
lot of testing to balance [Ca++] & alk.

Or, you could add limewater, (Ca(OH)2) which is already a balanced
source of calcium & alkalinity, with no Na+ or Cl- residuals to worry about.
I think for one-time top-up or corrections, the use of CaCl2 is ok (I've
done it myself) but long term maintenance I'm not so sure about.

Here are the equations, if you chem nerds out there want them:

The Calcium Chloride scenario:
Ca++ + 2Cl- + H2O + CO2 --- CaCO3 (insol.) + 2Cl- + 2H+
Note the CO2 comes from the air & to a lesser degree the critters.

Here is the limewater scenario:
Ca++ + 2OH- + CO2 --- CaCO3 (insol.) + H2O
(This is where Justin commented on water molecules)

Remember, no matter how much calcium you throw at your tank, there is a
ton of CO2 in our atmosphere relative to your reef, and eventually it
will form CaCO3 (calcium carbonate) - whether you add pool CaCl2 or
limewater. The limewater method, or calcium reactors, or balanced
2-part additives just leave you with residuals a *lot* closer to NSW.

I guess by now you've figured out I like limewater....

Cheers,

RedDeerReefer
Geoff Norris


peter wrote:
Yep i add bi carb for the alk but im not 100% where your sodium
chlroide comes from ... I guess if i mix some together and
test for salt you might be correct but i've got my doubts..

On Thu, 02 Sep 2004 00:14:15 GMT, "Mike Imbler"
wrote:


The real problem is that ca is used as ca carbonate, and cacl only supplies
the ca part. You can also add baking soda sodium bicarbonate to add the
carbonate, and the resulting sodium chloride from the two additions just
adds to salinity.
Mike
"peter" wrote in message
...

Justin,
you have a good point here.. Are there any chemist's out
there who could shine some more light on the subject.

One assumption is if the solution (mixed with fresh water) is allowed
to sit for a period of time the chroide may gas off...(this is only a
guess though)



On Wed, 01 Sep 2004 18:11:21 GMT, "Justin Boucher"
wrote:


I think the bigger concern would be the chloride part of the formula.
Althgouth it would be much more potential than Kalkwasser, you would
consistantly be adding chlorine in the form of a chloride to your system.
That just doesn't sound like good news to me at all. You would then need

to

continually treat for chlorine rather than allow the hydroxide of

standard

kalkwasser form more water molecules.

Perhaps someone with more extensive chemistry knowledge can add to this.

Justin

"peter" wrote in message
...

Does anyone use Calcuim Chloride for calcium supplimentation. Ive come
across some sold from a swimming pool outlet and am interetsed to hear
of anyone who has done the same. Its very potient. Unlike kalkwassser
(made from Calcuim hydroxide) a solution make from calcium chlroride
can be made a lot more potient (about 20 X that of kalk). The only
concern is what other chamicals that may be in the pool grade calcium
chloride.