Newbie need help - Flow Question.

Hi all:
Anyone could help me on this please, thanks in advance.
My tank is reef tank (meant to be) about Main: 170G with sump: 40G
I have 3 return, with height and lenght of hoses, return flow rate about: 165 GPH each. I put 2 of Koralia3 (850GPH) in the maintank for flow. So total flows are about:
3x 165GPH = 495 GPH for water turnover. Plus
2x850GPH flows circulation.

I just wonder is the flow rate in my system too low or too high? - Also, how do you recommend for: Water turnover rate and flow rate in the reef tank? - What are the recommendation for those, I mean...

Sorry if my question is not really clear and make sense. But that all I can think of to put into words.

Thank you all in advance.

*Remember I had a question about some aptasia and bad hickhikers? - Those rock now are in seperate tank with some Berghia working hard on cleaning the estate now, hehehe... Look prety fun when they are "at work"