Actually, I e-mailed Jim about this about 3 weeks after I first got into the Aquarium. I'd hoped that the humming noise of the water pump/filtration could be integrated into the Aquarium. Maybe some day.
Little splashing sounds and that humming/droning to go with the bubbles would bump the realism for me.
Also I have to say that the bubble sound right now is scarily relaxing. Maybe Michael should try it with the sound turned up. I know I just about end up face-first on the keyboard after 5 minutes of listening to it.