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They both produce ozone. One does so using a U.V light. The other by using a corona discharge method. The Cd method is newer. Does that equal better? Well, maybe. I'm told by some that it produces more ozone for less money. I am led to belive that the UV bulbs will need to be replaced more often and can cost about $100 a pop. I'm told the Cd unit should last several years and can be swapped out for aprx $200. That being said, I am also told single most important feature of an OZinator regardelss if it's CD or UV, is ithat it should be running off of a 24 hour circ system. This probably dones't help you....and is probabaly just contributing to your confusion. Sorry. But maybe it's fodder for the pros to argue about