Without knowing what type, or if any, corals your planning, its a bit of a wag. Also, you need to know what headloss your return pump will suffer. That being said, around
10-20 Times turnover for FOWLR
20-50 times Turnover for corals (SPS
need more, LPS
med, softies etc less, TYPICALLY)
so 270 times turnover gives anywhere from 2700lph to 13,000lph.