if you want a reef tank most suggest a total of 10 x tank volume in GPH
. but this includes filter and sump/fuge returns. It is also suggested that it be from multiple PH
's as you want to create turbulance, high current.
As an example, you're looking for about 720 GPH
for your size tank. So, if you have a sump that returns 300 GPH
I would pick up two PH
's that can handle 200-250 GPH
and the three combined will give you what you need.