imo, depends what you are gonna keep... fish only, as much as you want, and dont cheat the fish like most do with fish only, the more flow, the better... softies and lps, a fair amount is fine, but you never want dead spots in any tank imo... and sps, well as much as you can get, but not direct as in right on a colony or frag... however sps, need it to be changing and whatnot (ie wavemaker, vortech, etc)... something controllable that alternates flow..