To investigate the inhibitory effect of additive Ca 2+ ions on the growth of CaCO 3 precipitates, the precipitants volume (V P ) and concentration (C P ) were varied in the range 50 -400 mL and 25 -75 mM, respectively. Also, for each combination of V P and C P , the concentration (C S ) of the Ca(OH) 2 solution was varied between 5 -15 mM. C S was only varied up to 15 mM, due to the limited solubility of Ca(OH) 2 in water, which is ∼18 mM at 23 • C. For comparison, some experiments were completed using ultrapure H 2 O in place of Ca(OH) 2 solution.