When I got my TDS meter about 6 months ago, it said to calibrate it right out of the box. I
used a small cup of distilled water, and set it to 0.

"pushed the membrane"? That I don't understand. (What is it this week? "get my
umbrella"..."push my membrane"...what's next? "Freeze Dried h2o?" LOL)

Can you test the water coming out of the RO unit before it gets to the DI membrane? If not,
you should certainly get 0 after the DI in a brand new unit. However, let the ran run for a
little while, don't measure the first cup's worth. My unit is almost one year old with the
same filters still and my TDS is 1 two days ago.

I'm going to change my filters soon, but I wanted to do a chloramine test with the old set
and then with the new replacements to see the difference.

Marc


livingrock wrote:

Hi,

I just bought a TDS meter (Spirit, I think, its at home), it reads 198
for the tap water and 6 for RO/DI output water from my brand new Kent
Hi-s RO/DI unit. What gives I thought that it should read less than
2. Do the TDS meters need
calibration, when new? Could there be something wrong with my RO/DI
unit. I pushed the membrane in as far as it would go 1/2"(although
the instructions said 3/4").

TIA.

Marc Levenson wrote in message ...
Sounds like you are talking about a TDS meter. I did this a while back, and
don't remember exactly how I figured it out......

Test the tap water. Get a reading. Mine was 277
Test the RO water. Get a reading. Mine was 7
Test the DI water. Get a reading. Mine was 0

Take the RO reading and divide it by the tap water. In my case, that is 0.025.
Taking that number from 100, I get 97.5% rejection rate.

Or maybe that is just Marc's fuzzy math. grin

Marc, waiting to be corrected again....

Timothy Tom wrote:

I have a couple of RO units for my aquarium (automated top-off unit,
and unit in garage for water changes). One of the problems that I
have had is knowing when to change the RO membrane. I just got off
the phone with Spectrapure, and they just started to sell a Dual probe
meter which helps to quantify the efficiency of the RO unit (I was
told that the DI portion of water purification systems require a
resistivity meter which this meter does not measure). I was told it
is a digital battery-powered meter which measures contaminants in PPM
in the supply water and the outflow water (after purification).
Supposedly you can then easily calculate the rejection fraction which
is a direct indicator of the efficiency of the RO membrane. Anyway I
ordered two of these which cost 27 dollars each. These units are not
currently listed on their online catalog so you will need to ask for
them.

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