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.