Ozone is an effective disinfectant killing bacteria" viruses spores mold and algae.

Ozone compare with chlorine:
Like chlorine gas high concentration ozone is a poisonous gas.
Unlike chlorine gas ozone won't stay put when you put in water it will turn into oxygen in 30 minutes at a pool water temperature of 25 degrees C (77 F) and faster in higher temperature.
Unlike chlorine gas ozone treatment water is odor-free won’t produce by-product won’t dry the skin or irritate the eyes won’t bleach hair or bathing suits.
Ozone also leaves the Ph balance of the water untouched and is much less corrosive to a pool liner than chlorine use.
Chlorine byproducts (Chloroform Bromodichloromethane Chloral hydrate Dichloroacetonitrile and Tri-halo methanes) found in swimming pools are linked to higher incidences of asthma lung damage stillbirths miscarriages and bladder cancer according to credible research conducted in the U.S. Canada Norway Australia and Belgium.

And many studies shown that ozone generator can effectively clean the pool and frees the water of mold mildew bacteria yeasts and fungi. They are also effective at neutralizing and removing bodily oils and other human contaminants in the water. It can completely instead of the harsh chemicals.
The last but not the least using a pool ozone generator also helps to reduce the overall maintenance costs of keeping a pool clean. The ozonator only has to be purchased once and reduces the use of chemicals so fewer supplies need to be purchased each season. Additionally since ozone is not as harsh to pool liners fewer repairs may be needed.
The cost of ozonator may vary based on the size and model being purchased. In most cases the price spent on the ozone generator is made back by reducing the cost of yearly pool maintenance.
However pool owners should keep in mind that a pool ozone generator is used for microscopic organism.