In conclusion, we have reported the first one pot quantitative and reversible polymorph turnover cycle between three polymorphs of a molecular compound by ball mill grinding: Form A can be obtained from either Form B or Form C under NG conditions; Form B can be obtained from either Form A or Form C under LAG conditions with MeCN; Form C can be obtained from either Form A or Form B under LAG conditions with water. We have shown that a contaminant is critical to enable polymorph transformations under ball milling conditions, even at the low concentration levels typical of commercially available chemicals. We have given evidence of the exceptional reproducibility and specificity of the size for each of the three polymorphs. XRD analyses of specimens of different polymorph transformation cycles, show that Form A has reproducibly the smallest crystal size (50 nm) while Form B is the largest (140 nm) of the three polymorphs. These experimental results are further proof that polymorph stabilities under ball mill grinding conditions are affected by crystal size and surface effects such as the stabilization or destabilization caused by interactions between the solvent molecules and the nanocrystal surfaces. Furthermore, we have described a newly-discovered polymorph (Form C) which to date has been prepared only via ball mill grinding; this may prove a productive general route for the discovery of new polymorphs of significant molecular entities.