An apparatus and method for maximizing the dissolved concentration of ozone in a liquid. The apparatus includes a dissolution tank having a pressure vessel configured to contain a treated fluid and at least one gas in a head space above the treated fluid, an inlet configured to permit passage of an untreated fluid into the head space, and an outlet configured to permit passage of the treated fluid out of the vessel; a gas supply system configured to transport the at least one gas to the head space; a fluid supply system configured to provide the untreated fluid to the tank; a bleed-off system for removing gas from the head space so as to maximize the dissolved concentration of the ozone gas in the liquid; and a discharge device configured to pass the treated fluid from the tank into the target liquid.