On my 120gal cube I run 2 tunze 6101s (3200GPH/each) and a dart (3600GPH) on a closed loop and I also use a Dart as a return pump.
So you're not over any limits but flow requirements are more based on livestock. I would say however you're under powered for flow due to the bare bottom, I'm not sure what advantage this gives you for only soft corals.
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