TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
When the pressure rises 25% over clean.

So when you first filled it and started it, that's your clean pressure. It should be the same after backwashing. Then you just watch the needle. If you run at 12, backwash at 15.

If you don't get a lot of crud in the filter, it might end up just being an annual thing.
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