PRO CAL 20+ is derived from Calcium Carbonate that has gone through a proprietary process to render it�s particle size to less than one micron and completely water soluble. This high level of solubility elevates PRO CAL 20+ above all other Calcium sources currently on the market as a nutritional Calcium source. PRO CAL 20+ also contains a plant derived protein Nitrogen that has been proven to facilitate uptake and transportation of Calcium within the plant.