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Randy1
01/30/2007, 02:57 PM
Just received my Hanna pocket TDS meter. Not really any directions with it. How should I interpret the readings? I know the lower the number the better. My ro/DI unit has all new filters now, it reads 0 TDS. As the filters age what is an acceptable TDS readings.

AZDesertRat
01/30/2007, 04:45 PM
You need to look at 3 numbers to determine RO and RO/DI efficiency and when to change filters.
First get a squeaky clean glass drinking water glass with absolutely no water spots of detergent residue that you can keep for your very own, I had to wrestle my wife for one! Fill it with tap water and record the reading. Triple rinse the meter and the glass in DI water and next test RO only without DI and record that reading. Again triple rinse with DI and then fill the glass with DI water and record the last reading.
Now that you have all of this you should find your RO only water to be somewhere around 96 to hopefully 98% lower TDS than the tap water and the RO/DI as you found should be 0. If you are not seeing a reduction in the 96-98% range with RO only then its time to consider replacing the membrane. A very good rule of thumb is for every 2% you increase the RO efficiency you double the life of the DI resin so a good membrane is imperative. When you start seeing a rise in DI TDS above 2 or 3 its time to replace the resin. Prefilters and carbons have very little effect on TDS but they should be replaced every 6 months on a regular basis to lessen the chance of bio fouling or bacterial growth inside the housings. Its also a good idea to disinfect the housings with bleach when changing filters. I write the dates on my unit with a Sharpie so I don't forget plus I keep a log book of my water production and quality for future reference.

Randy1
01/30/2007, 05:46 PM
Good solid advice, thanks