Retrofit apparatus for retrofitting an ozone generator to a spa, hot tub or similar facility is disclosed. Here, a fitting is threaded into an air inlet of a spa or hot tub, and covers provided for the water outlets to generally prevent outgassing. In another embodiment, an ozone-providing plug is provided to one water outlet of a spa or hot tub, with the air and other outlets being blocked. In addition, different configurations of ozone generator are disclosed. Particularly, one type ozone generator includes an inverted U-shaped apparatus so that heat from the ozone generator induces a chimney effect so as to cause the ozonated air to rise through a chimney and then settle into a selected area. Another ozone generator creates a low rate of airflow by "ion wind" in order to propel ozonated air into a system of piping in the absence of water flowing therethrough.