ok let me put it this way. If I want to optimise my sump's efficiency (say a 20 gallon tank), is there a way to figure out what maximum flowrate I can have in the sump (regarless or what size display tank is going to filter)?
Lets say a 20 gallon, I would say your looking at around 600-800 gph give or take a little bit. This is the backwards way of doing it though, you first want to have an idea of how much water should be draining and pumping through your display, and what your plans for the sump are, refugium, strictly skimmer etc because flow somewhat varies from different applications/size of equiptment, narrowing down from this your then able to decide what size sump you will need.
Well thank you all for your help.
Sir Patrrick made some comments that got me to the point of rethinking my sump design and whole mechanichal filtration system. Thus It's back to the drawing boards for me. Thanks for all the info.