A cascade mixer and a valve mixer were applied for the precipitation of CaCO3. This model reaction has been used for benchmarking both mixer types with respect to their robustness against fouling. The valve mixer was found to be much less susceptible to fouling and clogging. Pressure changes during precipitation in both types of mixers differed significantly. This parameter can be easily used for identification of clogging in the valve mixer and applied as input in clean-in-place (CIP) procedures. The pressure trend in the cascade mixer is quite complex and, therefore, difficult to apply for CIP. Ultrasonic treatment has been evaluated as a measure to prevent clogging.