TDS lower than Salinity?

[J.ven]

I’ve tested my salt water pool using a Taylor TDS drop test, TDS Electronic Meter and a Taylor Salt Drop Test. The TDS tested at 2850 ppm and 2900 ppm on separate tests with the Taylor drop test while my electronic TDS meter reads 2890ppm. The issue is that my salt test tested at 3200 and 3400 ppm multiple times with a combination of different testing agents (2 of each = 8 different combos) all giving the same result. Even my SWG is showing between 3400-3500 ppm.

I understand this to be impossible, am I wrong? What conditions could cause this to happen?

 

[JamesW]

You have to know what TDS components are assumed to be in the water and what units the TDS are reported in for each different test.

If the test's assumed components are incorrect, the test is not accurate.

You also have to consider the reporting units.

If different tests use different reporting units, you would have to convert to the same units.

 

[AUSpool]

I’ve tested my salt water pool using a Taylor TDS drop test, TDS Electronic Meter and a Taylor Salt Drop Test. The TDS tested at 2850 ppm and 2900 ppm on separate tests with the Taylor drop test while my electronic TDS meter reads 2890ppm. The issue is that my salt test tested at 3200 and 3400 ppm multiple times with a combination of different testing agents (2 of each = 8 different combos) all giving the same result. Even my SWG is showing between 3400-3500 ppm.

I understand this to be impossible, am I wrong? What conditions could cause this to happen?

Geday J.ven and welcome to the FTP forums.

If your SWG is happy your good to go. If by Taylor salt drop test you mean the K-1766 then that is the number I would use. It directly measures the chloride ion which is the salt part of the salt.

Don’t mix reagents, just follow the instructions for each test.

Your electronic TDS meter needs to be calibrated. Ideally to something close to what your testing, a 3000ppm salt solution would be best. Without calibration its just a random number display, good for lotto numbers maybe.

For salt I round to the nearest 100, anything lower is just a best guess.

 

[J.ven]

The reason why I’m concerned with TDS as opposed to just the salt is because I am keeping my pool within LSI calculated parameters and the LSI is calculated with TDS. And I would figure my TDS would be closer to 4000 as opposed to the approximate 3000 as being tested since my salt is at 3200 and isn’t accounting for the other TDS components. The Taylor TDS drop test reports units as ppm CaCO3. If that isn’t accounting for all TDS what’s the best way to test for that?

 

[JamesW]

Just use your salinity result and don't worry about TDS.

 

[J.ven]

Just use your salinity result and don't worry about TDS.

Thanks for the help!

 

[JamesW]

The salinity reading does account for most of the TDS.

The salinity reading from the K-1766 salt test accounts for all sources of chloride, including sodium chloride and calcium chloride.

The conductivity test for salinity accounts for all TDS. It just reports it as sodium chloride even though it's not all sodium chloride.

The Aquarite cell performance salinity test accounts for all sources of chloride.

Your TDS is not going to be significantly higher than your salinity test.