Very nice, a quite formal appearance Jonna.
As for Dieffenbachia, I haven't found any reference as to them liking their feet wet all the time. They are not listed as a bog plant either. I believe they grow in forest jungles which is usually well drained humus. Also I'm sure you are aware they contain a toxic sap so that might not be good for the fish especially if they start to deteriorate. I would suggest Cannas, they have a similar leaf shape and size and they will grow in water (discussed in another thread).
