I run my Omega 150 in about 7 inches of water and with the adjustable venturi out two turns or so. Skims great for me. Lots of dark smelly crap. My daughter commented on the smell as I cleaned out the cup earlier tonight
While Vertex recommends that they can be run as deep as 9" my experience is that they do far better in shallower water. That seemed to be the problem with the Omega 130 as well which worked best at about a 6" depth. As I said, they are also quite sensitive to buildup in the volute and venturi too so those should be cleaned regularly. That's easy since the whole thing just twists off the front of the pump.