Test results change if sample sits after testing

[George in Georgia]

I've been using the Taylor DPD kit via Leslie's. I've also diluted the test sample 1 to 1 and then doubled the test result when the test results went off the scale. It would be nice if the Cl test were a "clean" titration with an easily discernible endpoint, as is the Taylor test for total alkalinity. Anyone who took college chemistry knows what I mean by an easily discernible endpoint.

Question: I've occasionally left the Cl tested sample capped in the test cell sitting out for several hours. After this time the reading seems to have climbed quite a bit. Does this mean anything? Also I have the Taylor salt test, which indicates much more salt than does the SWG board, the Taylor test gives 4900 ppm, as compared to the cell reading 2800 to 3000. Leslie's has as salt test meter which agrees with my SWG board. Any thoughts on this large discrepancy? A few hundred ppm I'd attribute to margin of error, but almost 2 to 1 seems a bit much.

 

[mknauss]

Re: Easier way to test chlorine when maintaining higher FC

I've been using the Taylor DPD kit via Leslie's.

Obtain a FAS-DPD test kit.

 

[Dirk]

Re: Easier way to test chlorine when maintaining higher FC

Also I have the Taylor salt test, which indicates much more salt than does the SWG board, the Taylor test gives 4900 ppm, as compared to the cell reading 2800 to 3000. Leslie's has as salt test meter which agrees with my SWG board. Any thoughts on this large discrepancy? A few hundred ppm I'd attribute to margin of error, but almost 2 to 1 seems a bit much.

It has been shown time and time again here: the accuracy of salt readings from SWGs is notoriously bad. Almost as bad as pool store results. Trust a Taylor test kit above either, for sure. Beware: salt tests have pretty high margins of error, even the Taylor. Like 400ppm in the range we test, I think. So a result of 3600 could be 3200 or 4000. It's pretty bad. And SWG readings are subject to water temperature, which make them even less accurate.

That said:

1. Be sure your Taylor reagents are not expired. There should be an EXP date on the containers.

2. Be sure you are doing your math right. I had the multiplier wrong for quite a while before someone here noticed and corrected me. Re-read the directions.

3. Be sure you are testing correctly. The Taylor test has a different end point than most other Taylor tests. You drop, drop, drop. Towards the end of your titration, the solution will flash a brownish color (Taylor calls it salmon) after a drop, then quickly return to the milky color once it mixes in. That might happen two or three times. Then the next drop will change the color of the solution radically and permanently. That's the end of the test. You don't continue to put in drops trying to find the last drop that doesn't change the color any deeper. That's too far, and can be way too far. It's the very first drop that changes the color permanently that ends the test.

 

[domct203]

I've been using the Taylor DPD kit via Leslie's. I've also diluted the test sample 1 to 1 and then doubled the test result when the test results went off the scale. It would be nice if the Cl test were a "clean" titration with an easily discernible endpoint, as is the Taylor test for total alkalinity. Anyone who took college chemistry knows what I mean by an easily discernible endpoint.

The Taylor FAS/DPD will provide that titration endpoint, and will measure FC up to 50ppm in 0.5ppm or 0.2ppm resolution, depending on sample size.

 

[George in Georgia]

Re: Easier way to test chlorine when maintaining higher FC

It has been shown time and time again here: the accuracy of salt readings from SWGs is notoriously bad. Almost as bad as pool store results. Trust a Taylor test kit above either, for sure. Beware: salt tests have pretty high margins of error, even the Taylor. Like 400ppm in the range we test, I think. So a result of 3600 could be 3200 or 4000. It's pretty bad. And SWG readings are subject to water temperature, which make them even less accurate.

That said:

1. Be sure your Taylor reagents are not expired. There should be an EXP date on the containers.

2. Be sure you are doing your math right. I had the multiplier wrong for quite a while before someone here noticed and corrected me. Re-read the directions.

3. Be sure you are testing correctly. The Taylor test has a different end point than most other Taylor tests. You drop, drop, drop. Towards the end of your titration, the solution will flash a brownish color (Taylor calls it salmon) after a drop, then quickly return to the milky color once it mixes in. That might happen two or three times. Then the next drop will change the color of the solution radically and permanently. That's the end of the test. You don't continue to put in drops trying to find the last drop that doesn't change the color any deeper. That's too far, and can be way too far. It's the very first drop that changes the color permanently that ends the test.

Thanks for the user report! I'll re-test following your advice. I'd tried the salt strips; I consider them a waste of my money and time.

 

[Dirk]

Re: Easier way to test chlorine when maintaining higher FC

Thanks for the user report! I'll re-test following your advice. I'd tried the salt strips; I consider them a waste of my money and time.

It goes like this, ranked:

Taylor Salt Test Kit
Salt test meter
SWG
Pool guy
Pool store
--
--
--
--
--
--
--
Test Strips

 

[George in Georgia]

The Taylor FAS/DPD will provide that titration endpoint, and will measure FC up to 50ppm in 0.5ppm or 0.2ppm resolution, depending on sample size.

I looked up the FAS/DPD kit on Amazon, and ordered it. No more trying do match colors with my aging eyes and varying light sources. I think it should be the extra money in terms of avoided frustration.

 

[kimkats]

If you let the FC test sit it will trend back to pink/redish. Once it changes call it then and use those results.