On my 20 gallon long I have an Aqueon Power 30 filter. That's the one "intended" for 30 gallon aquariums. Since my 20-long isn't as deep as one of those larger tanks, the force of the water coming down from the filter pushes the sand substrate around. It doesn't create clouds of debris -- it takes a few hours to "dig" a hole so that the glass bottom is exposed.
If I had something to break the flow, I imagine that would work. I see lots of web stores with artificial plants, but nothing like a lilly pad that floats. I had thought I could just use some fishing line to the side of the aquarium to hold it in place.
Any one have a better idea than me?