Yeah that's probably old school advice from the single speed days. It stood the test of time, but could prolly use an asterisk. I've seen my PSI as low as 2. Not only would I not see the 3, it would be time to clean at a 50% increase.This may be a silly question, but when adding DE to a sand filter, I'm assuming the 1 PSI rise is at full pressure from the pump, not a lower speed?