I did my setup with MGOCPM and black flourite. I put in the hardscape (driftwood bolted to slate) and then added ~2" of topsoil, and a little bit of water to help moisten it, and poked/prodded it around to get it in the gaps and get out air pockets, break up clumps, etc. Then I added the ~2" of flourite, and added enough water to thoroughly wet the soil layer.
Then I planted, and slowly added the rest of the water (poured onto a large filter sponge about a liter at a time).
I think the black color of the substrate helped a lot, as I didn't notice too many floating bits.