TDS meter calibration

[Hobster]

Randy,

My TDS meter is now reading about 20ppm for ro/di. As the Ro/DI unit is fairly new and has less than 200 gal of production, I suspect the meter is off. It did read 0 before.

It says to calibrate with 343 ppm NaCl which I can not find??
It shows this conversion.

SPECIFICATIONS
NaCl solution
Available in 342 ppm or 1000 ppm
3 oz. bottles (88.7 ml)
Solution Conversions

342 NaCl =
362 as KCl 478 as "442" 700 Ã"šÃ‚µS

--------------------------------------------------------------------------------

I am not sure what this means? What can I use to calibrate??
Thanks

 

[Randy Holmes-Farley]

In general, I doubt you need to calibrate. But if you want to, you can use any solution intended for that purpose. There are actually different ppm TDS scales, as I discuss in this article:

What is TDS?
http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.htm

The DI may be being depleted. Try inserting a new DI, run a few gallons through,and check the reading.

This article has more:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

 

[Hobster]

Using the chart in the first article. If I used a standard such as:

1,413 Ã"šÃ‚µS/CM Solution (for conductivity electrodes, 220 ml)

Would that equal----- 702.1 ppm and I calibrate to that reading??

 

[Randy Holmes-Farley]

Yes. Or you could set it to either of the other two values listed. You can use any scale you want. Like deg C vs deg F vs K. Overall, folks using it for RO/DI water need not calibrate, IMO. Calibration changes the slope of the resonse, not an offset. So 0-2 ppm TDS changes hardly at all, and since that is the point that we care about, calibration makes little diffeence.

 

[Hobster]

I have received a single use test packet of 10 microSiemens.

So based on the chart (and package) when I test my TDS meter in this solution, it should read 4.7 ppm TDS or do I multiply times the .47 factor?

As my meter only goes to whole numbers I am guessing I would calibrate it to 5 ppm?

Is this correct regardless that the solution is potassium chloride?



Thanks.

 

[Randy Holmes-Farley]

Setting it to 5 ppm TDS is a fine plan.