DE in sand filter question

[Deacon_Boogie]

I'm experimenting with adding DE to my sand filter to help with filtration of dead algae. I add one cup of DE mixed with water to the skimmer, which increases the pressure from 15psi to 16psi. Over the next few hours, the pressures rises, as expected. When I turn the pump off for a bit though ( e.g., when it cycles off overnight,) the pressure upon start-up returns to 15psi. I was expecting the pressure to remain elevated until I backwash. Why does the pressure drop when the pump is turned off for a while?

Thanks!

 

[JoyfulNoise]

That's the pressure at start up ... what does the pressure do for the rest of the time the pump is running? Does it climb back up over 16psi?

 

[Deacon_Boogie]

That's the pressure at start up ... what does the pressure do for the rest of the time the pump is running? Does it climb back up over 16psi?

It seems to stay at the start-up pressure. This morning the pump came on at 15psi at 8:00am (It had been at around 22psi when it shut off the previous night at 8:00pm.) At noon, it was still at 15psi, so I added another cup of DE. It quickly shot up to 20psi, and has remained there. Very confusing. I'm going to backwash it, start fresh with one cup of DE and let it run overnight. It just seems that once I turn the pump off for more than a few minutes, the pressure drops and doesn't come back up to the previously elevated level.