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Re: calcium carbonate source

On Mon, 29 May 2000, Bailin Shaw wrote:
> Roger, you said that you used calcium tablets.  Where did you get these 
> tablets?  Are these the calcium supplements you can get from the store?  
> Also, I have potassium sulphate instead of potassium chloride.  Would this 
> be a good alternative.  TIA.

Before you go further, make sure you have the right recipe.  The recipe I
posted originally had an error in it.  The right recipe was posted on
August 8, 1999 in a reply to Kevin Zippel.  It's at


I use calcium carbonate supplements from the grocery store.  Look for the
purest, simplest ingredients list.  What I bought are "Sundown" brand and
they do contain a few added ingredients (coating, and something that lets
the tablets break apart quickly when the coating is gone).  Avoid
chewables or flavored tablets.  If you can find some premeasured source of
powdered pure calcium carbonate, go with it.

It isn't easy getting the calcium carbonate to dissolve.  One method that
someone is using (I'm sorry, but I can't give credit where credit is due
here, because I can't find the author's original letter) is to dissolve
the ingredients in a gallon of water using excess calcium carbonate,
allowing the undissolved calcium carbonate to settle, then mixing the
settled solution with the RO water. It will take a little experimentation
to get the right amount of calcium carbonate that way.

Another possible way to do it might be to mix in everthing but the calcium
carbonate (the mix should have 1 degree of general hardness due to the
magnesium), then filter the mixed solution through marble chips or some
other reasonably pure source of calcium carbonate until the total hardness
reaches 3 degrees.

There are other people using the recipe who might be able to suggest other
The ingredients in the recipe are chosed to provide a reasonable balance
of all constituents.  You can't make any substitutions in the recipe
without messing with the balance somewhere.  In the specific case of
substituting potassium sulfate for potassium chloride, sulfate is already
provided by the epson salt so the potassium sulfate will overbalance the
amount of sulfate in the water; chloride (an essential plant nutrient) is
provided only by the potassium chloride, and the chloride will be absent
if you don't use it.

If you can't find necessary ingredients, it's possible to buy USP grade
chemicals in fairly small quantities from several suppliers online.  I
haven't done this yet, so I don't know what pitfalls and drawback there
may be.  I checked Spectrum Chemical, and their prices seemed reasonable.
This isn't a plug for Spectrum, there are other suppliers.

Roger Miller