Conductivity TDS Numbers

[Diver_1298]

I just received the EC/TDS meter that I bought from my local Grainger supply.
Here is the link. HI98311 Hanna Instruments with automatic temperature compensation. Grainger.com
I tested my tap water from my faucet, which has a 5 micron carbon filter on it.
Test results were 145 PPM at 80 deg F
I then tested my 30 gallon bucket of RO/DI water.
Test Results were 4 PPM at 77 deg F

These look like good numbers to me. But since this is the first time I have tested my water ( I know Duh ) I wanted to know what the experts thought...
Thanks for any replies.


Jim

[Boomer]

The meter numbers "may" not be in line and you may be better than you think but could also be worse. Did the meter come with a calibration solution. If so what does it say on the bottle ? And did you calibrate it ? If not we need to fix that.

So far those numbers look like your DI unit is going as it should be 0 ppm. But the meter offset could be that much.

[jtReef]

Looks great to me. I was always under the understanding even with just an RO anything under 100 is acceptable. But as usual the lower the better.

[Diver_1298]

Originally Posted by Boomer

Did the meter come with a calibration solution. If so what does it say on the bottle ?

No, it did not but I can buy one from the same place I bought the meter

Originally Posted by Boomer

if not we need to fix that.

I can do that The meter can be calibtrated to different solutions. I thought it might be a little overkill but I also wanted it to be versatile.

Thanks,

Jim

[Diver_1298]

They have the 1413 microsiemens/cm solution @ 25 deg c
Do you know the conversion factor to PPM?
I guess I'll google for it

Jim

[Boomer]

Jim

There is none. A conversion from uS to TDS is a non-linear conversion which requires a complex equation but there are tables. In ruff terms uS / 2.1 = TDS. So that 1413 = 705 ppmTDS as NaCl. For your needs that value is way to high and will impact the accuracy of the meter. For your tap water and RO/DI testing you want be be no higher than 300 ppm TDS.

There is also a second issue. Most calibration solutions are Sodium Chloride (NaCl). But there are also others i Potassium Chloride ( KCl) and 442 These can make a huge difference in the real reading. The proper calibration solution to get for tap water, RO/DI water, streams and lakes is 442 or equivalent. Some let me explain what that means.

A Okaton solution WD-00653-4 = 447uS = 225.6 ppm KCl = 215.5 ppm NaCl = 300.0 ppm 442. This solution allows you now to calibrate the meter to any of these 4. For the 442 you just stick the meter in the solution and turn the cal screw until it reads 300.00.

The solution you have is a Okaton or equivalent. I use to have another link on 442 bit it s now dead

WD-00653-18 = 1413uS = 744.7ppm KCl = 702.1ppm NaCl = 1000 ppm TDS

So your meter should be calibrated to 1000 ppm TDS or 1413 uS. Again this is to high to get accurate readings. If you want to get the 1413 it is up to you but the meter will be off a tad. So how much is that ? Using that solution, meter calibrated to NaCl @ 702.1 ppm setting it will will read about 1.5 ppm to low and at the 442 setting about 4 ppm to low when testing your water. And as I said ther 442 is a more real reading of what you have in TDS

Here is an example of nonlinear tables
OMEGA ENGINEERING - Technical Conductivity and Resistivity


Oakton
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Oakton meters for pH, conductivity, TDS, ORP, DO, temperature, and humidity measurement

We have a full review of all this here in Randy's artilce on understanding TDS

What is TDS? by Randy Holmes-Farley - Reefkeeping.com

You may also want to look at the RO/DI artilce
Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

[Diver_1298]

"Solution, Calibration, Pk25, 84 Microsiemens Per Centimeter, 20Ml Sachets"
Great, good information. I found this cal solution which will be closer than the 1413 solution so it will be more accurate in the range that I will be using. It comes out to less than a dollar a pack. It will be interesting to see how much difference there is from the factory calibration to what I will see when the solution arrives. Thanks again

Jim

[Boomer]

:thumbsup:

Yes that will be good stuff especially for the RO/DI tests and tap water

Go back here Jim it is on this sheet. So set to 84 uS or 50.50 ppm TDS. I would put the meter in TDS mode and cal to 50.50 ppm 442/TDS
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