[Delphinus]

Welllll ... possibly but not necessarily. 22ppm on the output is not great but at the same time it depends on how much it is going into the membrane. If it's say, 50ppm going in and 22ppm coming out, that's kinda lousy but if it's 450ppm going in and 22ppm coming out (in the south I get those kinda #'s but I'm not sure what it is on the north side, our water is out of different watersheds) then it's still doing its job.

FWIW, I replace my prefilters around the 6 to 8 week mark and I get maybe 3 to 4 weeks on the DI. I use colour changing resin but I also measure the TDS coming out and anything above 0 to 1 sustained (a small burst) means it's time to change the DI.

When I run my RO I have to flush the membrane for a good 5 minutes. The TDS surge from having it sit idle in between runs can get as high as 600 to 800. I close the flush valve as soon as it reads <10.

So I guess the question about whether 22 is bad or not kind of depends. Was that a sustained reading or was it part of a surge? If you read again in 5 minutes after running is it still 22?

If it is reading 22 all the time then I would say it is time for a new membrane. Typically, you should get up to about 18-24 months out of a membrane but it also depends on how high the TDS is going in and how often it cycles on and off. It's better to get a good long run less often than many smaller runs producing the same overall volume.

HTH