Abstract: Gas mix installation (5) for use in connection with tanks (1) for biogas reactors wherein the gas mix installation comprises:•—a main pump (8) having respectively a suction side and an injection side, where said pump (8) is arranged externally of the tank (1)•—a liquid suction pipe (6) connecting the interior of the tank to the main pump's (8) suction side;•—an injector pipe (7) connecting the interior of the tank (1) to the pump's injection side;•—a gas pipe (10) connected between the injector pipe and a source of biogas (9); where said gas pipe (10) is connected to the injector pipe (7) externally of the tank (1).