discrepant chlorine tests

[houdini1]

Good morning. My pool is now open for the season 10 days. The water looks perfectly clear (but is still 65 degrees). Free chlorine test yielded 6 ppm with 0 cc's, but when I use the OTO test it registers no chlorine level. The ph is 7.6 , cya level mid thirties. Pool is 18,000gallon plaster. I'm using combination TCA and bleach for chlorination. Any ideas ?
Thanks,
Ann

 

[JasonLion]

TCA?

The OTO test is a much more reliable indicator of chlorine/no chlorine than any of the other tests, all of which can be affected by other chemicals on occasion.

Which test did you use to measure FC 6 CC 0?

 

[houdini1]

I'm using the dpd powder and 871 to test chlorine from the tf-100 test kit

 

[duraleigh]

Which reagent did you use for the OTO test R-0600 or R-0003?

 

[houdini1]

It's the taylor k-1000 that came with my tf-100. I don't have the bottle with me now so I'm not sure-but looks like the 0600 in the picture online

 

[duraleigh]

The R-0003 reagent looks identical and is the incorrect reagent.

If you correctly used the R-0600, is it colorless? If not, it has been out in the sun and is not good any longer.

 

[houdini1]

It is colorless. It lives indoors inside the box, so I don't think it's been exposed to sun.

 

[duraleigh]

VERY unusual for the OTO test not to perform. Keep us posted.

 

[Killer95Stang]

I had this same problem last week. Since it was the middle of the week and not my complete testing day (Monday), I didn't use the DPD to backup my OTO test results. This caused me to basically shock the pool to 12ppm, before I verified that I had too high of chlorine.

In the end, I never really figured out what the issues were, although I did clean the OTO test comparator with dish soap right before I got better readings with it.

The moral of the story... trust your gut.. if the chlorine test seems too high or low, use the DPD to confirm.

http://www.troublefreepool.com/confused-with-chlorine-test-results-oto-vs-dpd-t58947.html

 

[houdini1]

Thanks everyone for your input. I just confirmed I was using the 0600 and it is absolutely colorless. It was registering chlorine levels when I used it a few days ago, but not as dark yellow as I should have seen with the level of free chlorine I was measuring using the dpd/0871 test which at the time was 6.5. Any ideas?

 

[Killer95Stang]

Only other thing I can think of is to shake the R0600 before using it. I never did that before I had any issues.

 

[duraleigh]

but when I use the OTO test it registers no chlorine level.

It was registering chlorine levels when I used it a few days ago, but not as dark yellow as I should have seen...

Was it registering SOME chlorine or NO chlorine?

 

[houdini1]

There was the palest shade of yellow, so I would call it a .5, if that's considered any chlorine

 

[duraleigh]

PM sent

 

[Killer95Stang]

There was the palest shade of yellow, so I would call it a .5, if that's considered any chlorine

When I was getting false readings... that is exactly what I had... I estimated it at 0.5ppm. Since we had a little rain and it had been hot, I figured the Chlorine was that low, so I added some Chlorine. Next day I ran the test again with the same result... So I added some more Chlorine. Right as I put the last drop in the pool, I thought I should do a DPD test. Wow.. the results were at 12ppm..

 

[duraleigh]

As a rule, it is a good working plan to test with the OTO test for the presence of chlorine....I would not use it for dosage.

If the OTO results are strange, do the FAS/DPD test to confirm your exact FC level and then dose.