You want 10x turnover through your sump each hour. So assuming that your return is feeding both your sump and fuge, you'll need to target +/- 600 gph. You can use a pond pump or anything really, just need to make sure that you account for the flow loss due to height. The higher it has to pump, the less gph you get. most pumps give you a scale of their rating. You should buy a little bigger than you need and you can always restrict flow with a ball valve if you need, but it's better to have too much than not enough and most pumps are rated based on perfect conditions and your tank will not be "perfect conditions" as soon as you start getting detritus and algae. A lot of us use Quiet Ones pumps cause they are cheap and reliable. Also realize that you need +/- 30x turnover in your tank every hour, so if your return pump is rated at 600gph then your 180 will be sitting at 3.3x per hour. Obviously not enough. You'll want to get yourself some powerheads to get the increased flow you need. you target gph in your display should be +/- 5400 gph.