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> Date: Sat, 2 Sep 2000 12:18:10 EDT
> From: Bob Dixon
> Paul Sears writes:
> << It _may_ effect the following reaction in hard water:
> Ca++ + 2HCO3- -> CaCO3 + H2O + CO2
> > That _is_ consistent with Merrill's observations e-mailed
> > to me in late 1998.
> That asumes Bicarbonates. If indeed it did affect hardness like this, it
> would handy for people trying to soften their tanks, and the resultant
> in KH would be measureable by someone who has used the thing for more than
> month, even with regular partial water changes. But what about pure
> carbonate solutes like Ca(CO3)2? Would we get?:
> 2 Ca++ + 2 CO3 ----> 2Ca + O2 + 2CO2
> This could be handy, and I would buy it for sure if that is
> how it works. I would drop it in a barrel of water and after
> GH and KH drop far enough I would use the purified water
> for my apistos and angels, and maybe even start
> keeping discus.
> Someone let me know if this is what's happening. It may be
> slower than De-ionizing but cheaper in the end.
Not quite right. Both Calcium (Ca) and carbonate (CO3) ions are divalent, so
your starting point would be Ca(HCO3)2, as Paul wrote. The breakdown to
carbonates and CO2 along the lines of
Ca++ + 2HCO3- -> CaCO3 + H2O + CO2
is the same path that occurs in both biogenic decalcification and "boiling
off" temporary hardness.
You don't start with "straight" carbonates because in the pH ranges of most
aquaria, all but a minute percentage have been converted and predominate as
bicarbonates. And once oxygen and carbon are formed to CO2, it is *very*
difficult to separate the oxygen back out again without expending a great
deal of energy.
If you're quick enough to filter out the precipitates, then the CaCO3
(including its calcium) would definitely be pulled out. Otherwise, as the
water reabsorbs CO2, everything would revert back to its previous state.
I would hazard a guess that if the "Carbo-plus" is acting along these lines,
scaling and precipitates would be problematic...
David A. Youngker
nestor10 at mindspring_com