Oclt is overrated

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Lemonhead

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Jun 3, 2020
101
Middletown NY-211
I hate to complain when everyone here has been very helpful. But when doing the oclt test I wanted to be sure my numbers were right so I did multiple fc tests and they come back different every time. The difference was more than 1ppm so the oclt test is invalid imo. I was getting between 20 to 24 drops. After testing 5 times and getting 5 different results I decided to save my reagent.
 

duraleigh

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Accuracy of the test works for thousands and thousands of people

What do you describe as the end point for that test, please
 

RMcGirr83

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Nov 19, 2018
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The OCLT is a method to determine something. If the only two things that consume chlorine are sunlight and organic matter how could the OCLT possibly be invalid if the method itself is performed correctly?
 

crimson avenger

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Jun 22, 2019
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I hate to complain when everyone here has been very helpful. But when doing the oclt test I wanted to be sure my numbers were right so I did multiple fc tests and they come back different every time. The difference was more than 1ppm so the oclt test is invalid imo. I was getting between 20 to 24 drops. After testing 5 times and getting 5 different results I decided to save my reagent.

The error of the test is 10%, which is consistent with the results you’re getting. This is not an often-discussed issue in this forum. I had to do some digging myself when I was getting wildly different results for my first SLAM, above 10 ppm.
 

Dtkokay

Well-known member
Dec 31, 2019
385
Houston, Texas
I hate to complain when everyone here has been very helpful. But when doing the oclt test I wanted to be sure my numbers were right so I did multiple fc tests and they come back different every time. The difference was more than 1ppm so the oclt test is invalid imo. I was getting between 20 to 24 drops. After testing 5 times and getting 5 different results I decided to save my reagent.

You're actually raising a complaint about the actual chlorine test, not the OCLT. The chlorine test is just a way to measure chlorine, but that doesn't mean the OCLT test itself isn't valid.

The chlorine test is not going to be 100% repeatable for many reasons. Someone above said the test has a 10% margin of error. That's in line with what you're experiencing.

Also, how do you know you're putting in EXACTLY 10 ml of water every time? That's a very small volume of water to get right every time. You could use a 25 ml sample instead, which would be easier for repeatability, but you would use way more powder and reagent.

And more fundamentally, there accuracy and repeatability are two entirely different issues when it comes to testing, which is a whole other topic. But I suspect what you describe involves both.
 

setsailsoon

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Maybe try a sample sizer? Works pretty well for me. Seems like it would at least improve repeatability and perhaps accuracy.
 

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Lemonhead

Well-known member
Jun 3, 2020
101
Middletown NY-211
End point of the test is when the pink water turns clear again. At least that’s what I try. It’s not an exact science if your off after testing repeatedly. Therefore the overnight test leads to inaccurate results no ?
 

tim5055

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End point of the test is when the pink water turns clear again. At least that’s what I try. It’s not an exact science if your off after testing repeatedly. Therefore the overnight test leads to inaccurate results no ?
Actually, if the test is performed correctly, yes it is an exact science.

The end point is when it turns clear the first time, not clear "again". If left to sit, a sample will almost always turn pink again. If you are adding more drops at this point we have forun your error.
 

duraleigh

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Well, pretty close but the way to get a precise endpoint is to continue to add drops until the last drop you add results in NO FURTHER color change....none......nada. That may help a bit.
 
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Lemonhead

Well-known member
Jun 3, 2020
101
Middletown NY-211
Wow you guys are really defensive over the chlorine test. I was just stating what happens if you take the test back to back to back.
You’ll get 3 different readings. No need to tell
Me im
Doing it wrong . I can see color change . I can count . I can read 10ml line on glass.
 
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