AquaCheck Salt Test Strips vs Lamotte PockeTester EC/TDS/SAL

[purptiger]

Hi, Mr. New Poster:

I have both of these items and want to kinow which do you think is more accurate for measuring Salt in my pool. The strips say that my SAL is 4500 ppm while the Tracer indicates 4180. The tracer is newly calibrated to 12880. Thanks, purptiger

 

[chem geek]

Welcome again.

Well, that's a tough call. Though fresh AquaChek test strips usually come out with reasonable accuracy, we have had reports of inaccurate readings, usually too high a reading on the test strips and that seemed to be more likely at higher salt (perhaps TDS overall) levels. A recent discussion about this is in this thread. The Taylor K-1766 you can purchase here at tftestkits.net might be better, especially if you use the 25 ml sample size where each drop represents 80 ppm.

My gut feel is that your LaMotte tester, properly calibrated, is possibly more accurate. If you can afford to get the Taylor test, it would be interesting to compare against it.

For readability, there is a forum rule not to exceed 5 lines in a signature so if you could combine some items onto single lines that would be helpful.

 

[JasonLion]

Keep in mind that both of those tests are +-400 or more, so those reading are completely compatible with each other.

 

[chem geek]

This page says that the accuracy for the LaMotte EC/TDS/Salt Tracer PockeTester is +/- 2% FS where "FS" means full scale. The relevant range in an SWG pool would be the 1.00 to 9.99 ppt so 2% would be 9.99 ppt * 0.02 = 0.2 ppt or +/- 200 ppm.

The resolution on the AquaChek White salt test strip is perhaps +/- 0.2 which corresponds to around +/- 250 ppm near 3000 ppm. I can't find any source giving an actual accuracy for this test.

So if the LaMotte were reading off by up to 200 ppm in one direction and the test strips were reading off by up to 250 ppm in the other direction, then the test strip and digital tester would both be well within their range of accuracy for what purptiger was seeing, just as you were saying.

NOTE: The EC/TDS/Salt seems to just be a conductivity tester that happens to have three scales in Siemens, TDS and Salinity. The TDS appears to assume only sodium chloride salt equivalent so will generally underestimate actual TDS by 100-200 ppm since the calcium is heavier than the sodium and bicarbonate is heavier than chloride. Not a big deal since the SWG really cares about conductivity anyway. The Taylor salt test, however, tests for chloride ion and reports the result as ppm sodium chloride. So this will also underestimate actual TDS -- again, not a big deal.