IMO, don't waste your time. 5.2 is a PH buffer and will not necessarily reduce your PH. In most cases the grain bill alone will reduce your PH by itself.
There are a lot of threads on this site regarding the use of 5.2 and its lack of ability in doing what people believe it to be designed to do.
There are better means of reducing ridiculously high PH's that you can read about in the brewing science section.