Help please--Circulation FOWLR

I have purchased my first sw aquarium. My set up is as follows. 75
Gallon All Glass Aquarium/ stand, drilled with overflow box. wet/dry
filter with in-sump EuroReef Es5-2 Protein Skimmer. Rio600 for pumping
water from sump back to the tank. 1 max -jet 600 powerhead (160 gph)
for circulation. 88 lbs of Fiji live rock, heater, etc. My problem is
this. The shop says the one Powerhead is enough for circulation but I
just finished reading The New Marine Aquarium and it indicates that
you need 5-10x tank volume /hr circulation through the powerheads. Who
is Right? should I get another Powerhead ?

Thank you

Russell