GPH your opinion how much?

[icedone]

hey all,I am gonna install a sump so I can eliminate my xp3(too high of nitrate trap).I have a 75g FOWLR but gonna make a reef.Is there a rule of thumb or a in your opinion answer on the GPH return pump.I have a fuge on it (10g)but I want it as a 2nd display.I was thinking of using my empty 40g for my sump.

[ccCapt]

You want aprox 5-10 times of your total water volume going thru your sump. So with a 75g, you are looking at anywhere from 385gph to 750gph.
Flow inside the tank is another story. You can go up to 40 times or more of your tank volume for SPS corals. You can easily use 2 K-4's in your tank.

I have 4 K-4's and 1 K-2 in my 125 for a total of aprox 5400 gph, not counting my returm pump.