Calcium Carbonate, or "Lime" is a common soil amendment, used for adjusting soil pH and providing Calium and Magnesium to plants. It is not significantly hazardous for the aquatic environment, but it increases the "hardness" of water. Harder water requires more soap to make lather, and results in insoluble scale around water fixtures.
As
CaCO3 
:
:
;pH
;Water Quality
Calcium Carbonate:
Calcium carbonate is an inorganic compound that occurs naturally as chalk and limestone. Its very slight solubility in water is a chief cause of "hardness" in water (ref).