I don't think a riccia wall would work very well either, also when riccia grows long bits break off very easily. After a while you would likely have lots of riccia floating around the top. To get a riccia carpet is really easy, just secure some riccia to some flat stones or stainless steel mesh. A lot of people use hair nets and such to attach riccia. I just used cotton thread and its working out just fine, the riccia covered it up and you can's see the thread anymore.