Very high doses of ozone will cause the plastic to get brittle over time but low doses will cause no damage. In general the modern school of thought is to use very low doses, on the order of 1 mg/hr per 20-50gallons, this is enough to clarify the water but will not serve as a sterilant, a sterilant dose really needs to be added in a reactor since skimmer function will practically cease with such a high dose.