To all owners of real property, as shown on the current tax duplicate, located in the state and within 200 feet in all directions of the property which is the subject of such hearings; provided, however, that this requirement shall be deemed satisfied by notice to the condominium association, in the case of any unit owner whose unit has a unit above or below it, or horizontal property regime, in the case of any co-owner whose apartment has an apartment above or below it. Notice shall be given by serving a copy thereof on the property owner, as shown on said tax duplicate, or his agent in charge of the property, or by mailing a copy thereof by certified mail to the property owner at his address, as shown on said current tax duplicate. It is not required that a return receipt be obtained. Notice is deemed complete upon mailing.