I'd build or buy a tank to use as a refugium and have it above the display tank rather than part of the sump. I'm still of the mind set that critters that should migrate from the refugium to the display tank will be killed by the pump.
I had my 90 gallon display with a 45 gallon refugium above and to the side (so the maintank/refugium made an L shape). The refugium housed peppermint shrimp, caluperas, a DSB and lots of live rock. The shrimp are always spawning so there are always little larvae around as food for the other stuff, corals etc. I found that with the refugium above my tank, my display tank always had huge numbers of pods running around, I could have had a mandarin fish in there no problem.
Doug
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