You really don't need that much constant aeration in that size pond. If you can't turn it down why not put it on a timer and just run it for 30 minutes or so every morning. You'll get the extra aeration when you need it, increase the circulation for a while to help move settled debris around in the pond, and it probably wouldn't be enough to hurt the lilies, in fact it might simulate the little bit of agitation they often get in nature wit wind and wave action.