Refugium help - need info and ideas

[Twinn]

My fuge would be about 5 gal so around 10% of the display. Don't know if could plumb it so DT water goes directly into the display. Either way if I just want the fuge to build a pod population what should I put in the fuge sand or no sand? If sand than how much sand? I plan to have about 1 1/2 inch of sand in the DT.