There are three methods used for the removal of hydrogen sulfide. If there is a heavy concentration of the gas, the water should be aerated, allowing most of the gas to escape into the air. Aeration of hydrogen sulfide requires that the pH of the water first be lowered to 6 or less, and then the gas can be scrubbed away by aeration. The remaining gas (or lower concentrations of the gas) can be oxidized by chlorine. Alternatively, ozone can be used to convert hydrogen sulfide to sulfurous acid, but ozone is also corrosive so it may cause as many problems as it solves.