I have a variable speed motor and pump.  It has 3 speed settings.  Each speed is set for a different RPM and duration.  The pressure of my filter varies quite a bit at the various rpm settings.  Given that, how due I determine at what pressure I do a backwash?  I have a DE filter.  I am used to a single stage motor so I was readily able see the increase in pressure.  Do I have to run the pump periodically at the rpms comparable to a single stage motor or is there a more intelligent way?  Still trying to get use to all these new benefits with a VS pump/motor.