Backwash when the pressure gauge tells you, not the calendar.

When the pressure rises 8–10 psi above your clean starting pressure. That’s it. No every-two-weeks nonsense.

Backwashing on a fixed schedule is how you waste water and DE. The filter doesn’t know what day it is. It only knows when it’s dirty. That’s what the gauge is for. Check it weekly, write down the clean pressure after a backwash, and only backwash when you see that 8–10 psi jump. Also watch the return flow — if it’s visibly weak and the pressure is up, it’s time.

One gotcha: DE filters are more sensitive than sand or cartridge. Over-backwashing (doing it when the pressure is barely up) actually reduces filtration efficiency because the DE grid doesn’t get a chance to build a proper cake. Let it get dirty enough before you flush it.

And don’t forget to add fresh DE after backwashing. The gauge will tell you when.