I use mud for all my setups and put a 1/2 inch of broken sea shells on the bottom before I put the mud in the refugium. This gives more area for denitrifying bacteria and critters to grow. Plus, when I add the mangroves in their tanks, it gives the roots an easier place to spread. When I fill up the refugium with water, to avoid a cloud in the DT, I place a glass in the refugium and let the glass overflow so that it just pours over and doesn't disturb it too much. Then I let it settle as I work on other things and then plug it all in and change out the filter pad when it gets dirty. I say MUD......