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The authors show that pH increase, due to removal by condensation of silicic acid, correlates with nanoparticle growth during the initial stages of silica hydrogel formation and becomes constant at a time tpH, the point when other particle growth mechanisms dominate. Absorption of common phthalein indicators is shown to allow effectively instantaneous tracking of the pH and nanoparticle size in alkaline and acidic hydrogels. Particle sizes are calibrated using the hydrodynamic radius determined from the fluorescence anisotropy decay. Tracking pH complements fluorescence anisotropy nanometrology by offering a lower cost, speedier, and simpler method of studying particle growth during silica hydrogel fabrication. [ABSTRACT FROM AUTHOR]