aquaclear 500 help

Sometimes impeller sucks in grain of sand or something hard like that in the shaft and then that object can grind and damage magnet badly to the point where it will start making noises or eventually stop working. Pull impeller out and see if there is any damage on magnet. It should be nice and smooth. Also clean shaft with brush and make sure that there is nothing inside. If magnet is damaged, replace impeller, but remember they can be pretty expensive. Sometimes the whole new filter would be only few bucks more than the impeller itself.