So, I've had some time to use my
TDS meter. What I found was that the output of my
RO/DI unit was not the pure water I was hoping for. Instead of having a low reading, close to 0, the output was measuring anywhere from 200 down to 40ppm. The longer the
RO/DI unit sat idle, the higher the reading would be. If I ran it for a long time the reading would drop.
My meter has two inputs. A slide switch selects which input is displayed on the LCD; in or out. I originally hooked it up to measure my water supply into the
RO unit, municipal supply and the output out of the DI that went into my storage container. My
municipal input has a
TDS reading of about 300 ppm. Since I can't control it and since it doesn't need to be monitored regularly I moved the
TDS in probe to measure the water out of the
RO filter
which feeds the input of the DI filter.
What I found was that the
RO output had a
TDS reading of 6 ppm. Since the DI output was varying between 200 and 40 it was obvious that the DI resin was actually contaminating the water rather than filtering it. Time to change the resin. The resin indeed was very dark but I never noticed it because the location of the filter is pretty dark.
So I ordered more resin from the
Pure Water Club on
eBay.This where I bought the filter 15 months ago. The
refill resin arrived quickly and I replaced the resin in the two
canisters. Now, my
RO/DI filter produces pure water with a
TDS measurement of 0 ppm.
The moral of this long-winded story is if your
RO/DI filter is more than 6 months old you really should get a
TDS meter to verify your water quality is what you think it is.