The rapid growth of KDP crystals was demonstrated at growth rates of up to 54 mm/day. Thermal and acoustic energy were used in the saturated solution to delete clusters of molecules. High supersaturations larger than 120% were achieved by overheating of the mother solution by 25 K. The application of acoustic energy to the solution was also used to achieve high supersaturation. The dissolution of the clusters in the solvent was discussed, explaining the rapid growth rates.