User blog comment:Silver-Haired Seireitou/Sake Time with Sei - Can Arrancar Use Kidō?/@comment-1493741-20140413171315/@comment-2089817-20140413172947

You have a point, although that argument hinges on the idea that Cero uses reiryoku, not reiatsu. Given that the nature of all the other Hollow techniques used by Arrancar, such as Bala, Hierro, and even Pesquisa, are all founded in the use of reiatsu, it is more probable imo that Cero is a reiatsu beam rather than one that uses reiryoku. It would also explain why Gran Rey Cero can distort space, because of the pressure and force having reached immense levels.