From an article on ozone in a reef tank:
Another method is ozone, a highly reactive form of oxygen. Injecting ozone into the water improves water quality by oxidizing large organic compounds. Although ozone can be effective, particularly if used with other methods such as activated carbon, hobbyists should be very cautious with it. Large amounts of ozone can be hazardous to both aquarists and tank inhabitants. Too much ozone can "burn" delicate tissue such as fish gills. Excessive ozone can be particularly dangerous in saltwater tanks because it reacts with some elements of saltwater, such as boron, producing potentially toxic compounds. Begin with very modest levels somewhat below the recommendations for your tank size and observe the tank's inhabitants. If any of the tank's inhabitants seem to be negatively affected, then ozone dosage should be reduced. It also helps to monitor ORP (Oxidation-Reduction Potential) levels to make sure they increase modestly and gradually. At proper levels, one should not be able to smell ozone around the tank. The odor of ozone is slightly sweet, like the air after a thunderstorm.
