My refrigerator has a carbon block water filter. I'm wondering when the proper time to replace it is, and don't want to replace it too soon.
Is using the pressure drop/flow rate a good method of knowing when to replace it, or should I go by the "months/gallons" rating, even though my city water might be cleaner than the water they used for the lifetime testing, so it wouldn't need replacement yet? Or will bacteria grow in the old filter, so I really should replace it every six months regardless of use?
What's the failure mechanism of the filters? Will they start to pass what they are supposed to block, or does their pressure drop increase while their filtering ability remains nearly constant?