Ozone is used as a water purifier by injecting it into your skimmer typically. It's a radical oxidizer that pretty much burns up anything organic from tbe water column. It's a great tool for the advanced reefkeeper, you can find more info in the 'Advanced Topics' forum here. I've been using it on my system for past six months and very pleased with outcome. Once again a advanced application with high risk if not properly set up and understood.
Cheers, Todd