For the sake of finding an effective and precise way to control crystallization processes a huge number of investigations was car- ried out in the past decades. Besides controlling the supersaturation in terms of the system temperature or adding seed crystals to the supercooled solution, the use of ultrasonic irradiation has become an interesting method to control the process as well as to influence the size distribution and the habit of the crystalline product (Ruecroft et al., 2005). Seeding and using ultrasound have in common that they lead to a decay of the slurry concentration at lower levels of supersaturation and consequently circumvent or at least affect the hardly controllable primary nucleation at high supersaturations.