Leng Sy continues to be a pioneer in the reef hobby. His patented miracle mud has been tested for contents but a duplicate product that works as well doesn’t exist. I spoke to him at his booth in reefapalooza and asked if mysis eggs were added to the mud, cause all my tanks and refugiums were full of them. He didn’t really give me a direct answer, only that the MM promotes them. I bought and used Fiji Mud years ago to compare with MM, it was not the same for reasons unknown.
A substrate that I have been using, not in the refugium, but in a 29 biocube is Two little Fishies, Refugite. As a dark aquarium substrate it is just as good if not better than live sand,it doesn’t compact, and stays clean. Someone mentioned magnetic particles in another product above. Not magnetic, it is actually iron oxide in the mix that gets picked up by a glass cleaning magnet.