I don't currently run a sump so I'm just going by what I've read, but typically the flow from your return pump and sump is insufficient for most marine set ups. It's more for filtration and extra water volume than for flow. Some folks run water faster than others through their sumps, but for hard corals, supplemental flow is almost always required, either via powerheads or closed loops.
Even though I don't have sps corals, I run two VorTech MP40Ws in my sumpless set up. The flow from these two powerheads does a great job of keeping detritus etc from settling anywhere in the system.
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