I believe the typical standard for a fish-only tank is to shoot for 10x turnover (10 times in GPH the gallons of your tank) so for a 65 g tank, you'd probably want to get at least 650GPH turnover. This number would also include the GPH of any filter pumps, skimmer pump too if you have one . . . maybe (I don't know if your skimmer pump GPH is factored in, but I don't see why not, it is turning water over in your system).
Probably wouldn't be a bad idea to instead of installing one PH to supply the necessary turnover, use two smaller ones so that you have more control over where the water is flowing and it's undoubtedly easier to deal with dead spaces.