[schildkoi]

As Papabear mentioned, Koi are simply inbred riverine carp. They do not need "still" water to rest nor should the constant hum of an airpump/airflow have any detrimental effects since sound waves in water travel very easily and if one thinks about a river, or even a lake, their are also noises. A koi will rest nicely in curents of 9in/sec and gently drift. Although a diffuser dome will create large currents and water flow, the exponentially decrease with distance from such.

Steve