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Better CaCO3 addition methods?

Justin Collins wrote:
        "I recently built the CO2 reactor from hell, and
was wondering if I can go to the drug store and buy the tablet form of
CaCO3, and put the tablet way down at the bottom of the reactor.  I'm
thinking that the increased acidity of the water before it leaves the
reactor will facilitate the dissolving of the tablets, and it would
a slow, gradual raising of GH and KH, which would help avoid and fish
shock.  Any thoughts?"

        I have thought about doing this too.  My one question is, once
high concentration CaCO3 mix in acid-water hits the regular, higher-pH
tank water, is the extra CaCO3 going to come back out of solution?  I
guess it would be easy to do a little experiment...  Also, it looks to
me like the biggest determinant of how fast the CaCO3 goes into solution
is its surface area.  I used to think that just letting the tablets fall
apart back by the filter intake would work, with the water streaming
over them. But what I got was perennial piles of chalk (until my
chalk-loving SAE
stirred them up, anyway.)  I wonder if you wouldn't get the same thing
at the bottom of your reactor (unless it's getting really acidic in
        George Booth's 'Aquatic Concepts" web page suggests spreading
the CaCO3
along the back of the tank at the base of the bunch plants and letting
it go into solution.  When I'd make up a slurry of CaCO3 and tank water
and kind of pour it out at the base of the plants, a lot of it still
clouded the water and raised the pH a couple or 3 tenths very quickly. 
Now I throw a couple of tablets into a great big syringe (a baster would
work too) and shake it up after an hour or so.  The 200 ml or so slurry
can then be slowly pushed out at the base of the plants, and not much
goes into the tank water -- much better control.  By morning it's all in
solution.  This is kind of a pain, but works better than anything I've
used so far.  I know you could just put some kind of carbonate material
in the filter and let it slowly dissolve, but I like the idea of being
able to add exactly the right amount of CaCO3 to the new water.
        I suspect for the people who have higher KH have less problem
with pH
change with CaCO3 addition.  I keep my GH & KH at 2, so I can get some
pretty dramatic swings if I'm not careful.
        CaCO3 is great stuff for those of us with mineral-free water,
but it's
a pain to add.  Any other thoughts?  Also, is there something that would
give both Ca and Mg?  Dolomite?
Sherman Lovell