Moderate flow is somewhere in the 30x turnover range. Let's say you have 50g of water in your tank. (Just in your tank; not your whole system.) When you add up the flow from your pumps and wavemakers, you'd want it to add up to 30 * 50. That's 1,500gph.
But that's deceptive, because you'll never have the same flow in every spot of your aquarium. Some areas will be higher flow (those right in front of where the flow is coming from), and some will be lower flow (behind rocks, etc.).
My goal is to make sure there is water flow through every spot in the tank so that things don't build up. After that, it's a dance between placement of corals and placement/strength of water-movers. If you want a coral in a specific spot, you see if flow is right there (by watching how the coral moves and/or behaves in that spot). If the flow isn't right, you can either move the coral or tweak the water-movers somehow.
