old salty
i haven't tested the output of the reactor, costs about 2 bucks a test
so i try not to get to carried away with it as long as the tank levels are dropping.
on my reefs they stay at 0.01 for several months, with a Salifert test kit i used to think the output of the reactor was always zero but with the meter i discovered it's not most of the time, even with new media.
with that said it would be my opinion you can't test the output of the reactor and get an inclination as to when the media is exhausted.