Dupla $tuff

Have been using Dupla's KH+GH tablets for quite a while with good

Thinking of switching to home made tablets and arrived at this posting
by George:

> One teaspoon (about 6 grams) of sodium bicarbonate (NaHCO3) per 50
> liters of water will increase KH by 4 degrees and will not increase
> general hardness.  Two teaspoons (about 4 grams) of calcium carbonate
> (CaCO3) per 50 liters of water will increase both KH and GH by 4
> degrees.  Different proportions of each can be used to get the correct
> KH/GH balance dictated by the fish and plants in the tank.  Since it
> is difficult to accurately measure small quantities of dry chemicals
> at home, a test kit should be used to verify the actual KH and GH that
> is achieved.

a)Is CaCO3 insoluble in water?
b)If so, will crushing them into powder form make it soluble?
c)Are these the only ingredient (NaHCO3 and CaCO3) that made up the
Dupla's KH+GH tablets?