Reverse osmosis desalination plants are to deal with scaling problems which canlead to the membrane destruction. This project studied the delay in CaCO3 precipitationduring ozonation experiments conducted on synthetic seawater. A reliable precipitationtest for seawater was developed since the reproducibility of the experiments was poor.Empirical models for bromate formation were used to give a bench mark for the ozoneexperiments. The main parameters to control bromate were the applied dose, contacttime and the water pH. Synthetic seawater samples were ozonated in a batch reactorunder satisfactory conditions to achieve a significant retardation in CaCO3 precipitation.Sonication was tested to cause a pH depression to a lower levels were the bromateformation is suppressed, but the acidification did not occur.