Sulfur denitrators don't release calcium and carbonate. The bacteria eat sulfur and nitrate in the water to make nitrogen gas. I believe the effluent is typically semi-acidic and some designs use calcium carbonate to raise the pH prior to feeding back into the aquarium. This results in some added calcium and carbonate. I think you may be thinking of a calcium reactor where CO2 is injected to lower the pH and dissolve calcium carbonate material and the calcium and carbonate effluent is fed back into the aquarium to maintain calcium and carbonate levels.