IMO it is not that much important how much flow you have from the sump to a display tank, as log as there enough flow to keep your "U" pipe clear from air bubbles if you have overflow box that is , it is way more important how much internal flow you have inside your display tank. To keep debris suspended and delivered to your skimmer via overflow.
So as long as you are delivering enough water for your filtration equipment that is all that you need in terms of return flow.
Internal flow inside your display tank is what matters most and that is what most pple have not enough of.
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