Amazon.com: Customer Reviews: HM Digital TDS-EZ Water Quality TDS Tester, 0-9990 ppm Measurement Range , 1 ppm Resolution, +/- 3% Readout Accuracy
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on March 27, 2014
I bought two of TDS-EZ Water Quality Testers and while both are placed in the same glass of water, the one reads 752 ppm and the other 371 ppm. You can only conclude that they have not been calibrated in the factory, as claimed on the packaging.

Photo here:
[...]
Poor show!
review image
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on December 29, 2012
Very easy to use and is accurate enough for my needs. Values match the values shown by the tds display on my RO unit's in/out readings to the DI stage.

Update: I have realized that there is a HM Digital TDS-4 Total Dissolved Solids Pocket Size Meter unit available on amazon for just a couple of dollars more than this unit. From what I can gather, the TDS-4 is essentially the same unit but has temperature compensation circuitry that does not exist in the HM TDS-EZ. I did a simple test to see if I could quantify the temperature effect. The effect appears substantial. I am reducing my rating from 5 down to 3. Here are my results using the same sample of tap water at different temperatures:
54 degrees: 220ppm
100 degrees: 404ppm
112 degrees: 434ppm
130 degrees: 540ppm
Plotting this on a graph reveals a linear variation.
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on June 28, 2012
First, this device works great and it can't get any easier. I did a few tests and the results were consistent. For quality, ease of use, and 2 years warranty, I believe it deserves 5 stars.

The sensors measure the Total Dissolved Solids (TDS), which are the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water in parts per million (ppm). However, I found out that water from the same source will measure differently when the temperature is different. For example, a room temperature water measured at 150ppm, but 110ppm when cold and 192ppm when hot. I thought its interesting.

I like the fact that in the back of this device, they put this sticker so you don't need to memorize anything:

How Pure is Your Water?
-----------------------
0-50ppm = ideal drinking water
50-100ppm = carbon filters, springs
100-200ppm = hard water
200-400ppm = average tap water
and so on

It also has protective cap to cover the sensors (not shown in the picture). It's factory calibrated and is ready to use, but can be re-calibrated with NaCl using a small Phillip screwdriver. Battery lasts for about 1000 hours and the instructions are clear with reference to the website if more information is needed. Overall, it's a 5 star item. No more guessing now!
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on February 20, 2011
This is a great unit, as soon as I got it my tap water in Vegas was 435 which is VERY high, so I tested some bottled water and it was 12, then I went a tested a few different outside water vendors and found a few that are better then bottled water, I have read a bunch of articles and they all way you should drink water 0-50 the lower the better as higher water levels are bad for you. This unit is great as pour a little in (DO NOT PUT THE WHOLE UNIT IN THE WATER, JUST UP TO THE WATER LINE) press the on button and read what it says on the large digital display, if you can not see it in the water, push the second button which will hold the reading so you can take it out of the water to read it.
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on June 1, 2010
Worked perfectly right out of the box.

I did a quick control test with three different waters right after turning it on the first time.

My one-minute test results:

Distilled pure water = <1 ppm
Plain tap water = 64 ppm
Sports water (Propel) = 260 ppm

I also received the unit within a couple of days, very prompt.
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on March 22, 2010
inexpensive and works every time. no calibration or battery changes needed in the ~6 months I've had it.
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on June 14, 2010
I've had this for about 6 months now.
I use it daily.
It's always accurate.
Never had a problem.
The auto shut-off is fantastic.
I'm very forgetful.
Even with all this use, It has not needed a battery change.
I use a lot of meters and this one is by far the most worry free of them all.
I would definitely buy this again.
TOTAL WIN!
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on November 12, 2012
The day this came in the mail I tested in distilled h2o which read 0-1ppm every time

Then I tested in the calibration solution of 342 and it was way off. It read 455.

So I recailibered the unit to 342. And rechecked was off +/- 5. Then I waited an hour and retested in the calibration solution. It was off more then 50ppm, so I recalibrated the meter waited an hour and it's was way off once more. After playing this game for 4 hours, I quickly packed it back up and returned it immediately!

If you need a accurate meter this is not it. The package says +\- 3 but i was not able to get these results with their own calibration solution is troublesome.
If you need this for a hydroponic setting I'd recommend getting a more reliable meter!
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on June 4, 2011
Just turn it on, dip it in the water for about five seconds and the same result every time. It made Ppm very easy to understand. Just get the NaCI 342 Ppm calibration liquid for the future. You will hardly have to use it. just dip the meter in the fluid and wait until the meter reads 342. It's solid also.
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on January 23, 2013
WAS OFF (70) USING THE 342 TEST WATER..SHOWED 412. TRIED TO ADJUST (TWEAK) IT USING THE MINI-PHILLUP SCREW
ADJUSTER AND IT GOT REALLY "WAY OUT" OF CALABRATION. SENT IT BACK.
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