resupinata has purple flowers too. Very different aswell...
What I did for an aldrovanda plant was I stuck a bubbler stone int he water, but pinched the air hose so that it was just small amount of bubbles coming up, as not to disturb the water too much... You could try that if u don't want a waterfall... Gibba is a subafixed too, isnt it?
When i saw the U. purpurea in the wild, it didnt seem that they need too deep water... They could grew in deep water, but on the hole, most flower stalks were around three to five inches tall... and the flowers sat just on, or above the surface... Ideally purpurea likes about five or six inches i'm guessing... Then again... It was the wild, so it does wut it wants, or dies..