I think you are more confused.
With a kalk reactor you want it sealed from anything getting in.. Top off water only mixing with the Kalk..
CO2 is used in a CA reactor to drop the pH of the rector so as to break down the Ca based media.
With Kalk you don't need to drop the pH to have Ca go into solution. It is already there once you stir it.
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Darren
Always strive for the optimum environment, not the minimum environment
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