I've got 2 sets and had the pool for 3 seasons (bought the 2nd set after a year with the 1st set).
Even after I've cleaned them and watched what looks like a pound or two of gray junk get washed out of them, they stay gray. I just finished an overnight soak in TSP (1 cup/5 gallons) and rinsed them out and they're *still* gray.
Yet, they seemed to be doing fine last year and my pool was crystal clear all season.
Am I still not cleaning them enough? How can I tell if they need replacing?
Is it a good test to fire up the pump at full blast without them, get the pressure, then fire up the pump with them and see what the increase is?
BTW - sorry I'm a constant flurry of questions lately...did I mention I'm opening my pool myself for the first time?