Usually a reef has anywhere from 20-30x turn over per hour. I have about 3200gph turn over in my 72g bow. I have a closed loop that puts out about 700gph, and I have 2 Tunze 6025s that move 660gph each. My return is moving close to 1200 gph
. The Tunzes are a far gentler PH and create a large swath of flow. The closed loop is plumbed through 1" pipe so it too has a larger swath of water flow.
The kind of flow you need depends on the kinds of corals you have. SPS
corals like more flow where as LPS
corals tend to like a little less flow.