Ideal return pump flow

[gregzz4]

I gather from, the 1,098gph you're calculating, that this only based on an empty 180, which probably still wouldn't hold a true 180g
My 75g only holds 62.75g ( 61 tank and 1.75 overflow box ) after 1" of sand and maybe 65lbs of rock

If your 180 holds only 165ish gallons, and your sump is 50 ( to be generous ), you would need a flow rate of over 1300gph

Maybe someone else has a better idea ...