Sorry, should have clarified. The epoxy itself encapsulates the individual grains, I then placed it in a form to mimic the shape of the biocube and it cured into a single large piece. The final product looks like a 1" thick black rice crispy treat. Because it is all stuck together, grains getting stuck in the magnet are no longer an issue. Once in the tank it looks like a thin layer of sand, and my powerhead shoots directly onto the sandbed and prevents detritus with no flurries.
Yeah I posted the project in my thread awhile back, but I never posted finished pics, this pic shows it before I place in tank. The dimples are to hold the rockwork in place. The second pic shows the scape. I did rotate the big rock about 2 inches to the right in the pic to fit right in the dimple.