Ozone oxidizes just about any organic matter it comes in contact with, much like chlorine does.
So any free floating algae, parasites, or debris are converted to carbon dioxide, water and disinfection by-products such as aldehyde.
It has a half life of 15 minutes in water, so it can be problematic if any is not used up before entering the tank, where it can damage gills and other organs.
Used in a protein skimmer that's effluent empties into a sump helps, or it must be quenched before entering a tank (some say filtering the ozonized effluent thru carbon can work, we used a calcium thiosulfate drip/injection to quench).
Although I have not used it in the aquarium, I was involved in using it for drinking water disinfection where it is excellent for purification of all the above constituents.
We use ozone in our plant as the initial disinfectant to kill protozoa such as Giardia, cryptosporidium, bacteria and free floating algae, before the filtration process.
Because our treatment flow was in the 100-200 million gal per day range, our ozone concentrations were high enough to be extremely dangerous to human health, and treated with high degree of respect.
Ozone must be manufactured on the spot, because of its short half life, and is made by running air thru an electric arc.
