I would stay away from the mud. It is expensive and when you have to change it out it is very messy. I used miracle mud for a while and it worked fine, but was so expensive I switched permanentely to fine sand and that seems to work fine also. If you want to do this a little on the cheap, a 6500K flood light from the 'Depot' works great as a refugium light. One thing with having a large refugium is that it reduces the need for a sand bed any deeper than 1 inch in the display so that is something to think about also.