Just thought I'd pass along that Tunze pinwheels work great in sicce pumps...better air draw, finer microbubbles and dead silent... I have a 9420 impeller assembly in my psk 1000 and the difference between the stock impeller is remarkable... best part... the impeller only cost 23 bucks vs a sicce at over 50. The Tunze pinwheels use a better magnet and have a lower delta vs sicce...the delta is the space between the shaft and the bearing the shaft rides in... lower delta = smoother running and more silent operation... great upgrade.