Cannot get accurate results out of TF-100 chlorine test for the life of me! What am I doing wrong?

[MalcolmV8]

So my pool had turned green while I was out of town and it was recommended that I perform a SLAM and then use the TF-100 kit for accurate results to complete it. Well I followed the basic recipe and bumped my FC levels up according to the FC / CYA chart and within 6 days it was crystal clear again. Now I wanted to perform the over night chlorine loss test and this is where it all fell apart.

The SLAM video says to take an accurate measurement the night before and then again in the morning and make sure you have no more than 1 PPM loss of FC. So last night I perform the test and then immediately tested it again, and again, and again, and 5 more times for a total of 8 tests and cannot get repeatable results. If that's the case how am I to validate in the morning I only lost 1 PPM?
Last night the number of drops in the FAS/DPD test to change the liquid clear was:
28, 30, 27, 32, 24, 30, 31, 29. So my FC was anywhere from 12 ~ 15.5 PPM.

Then this morning I ran the test 3 times before giving up. I already knew from last night I wasn't going to get anywhere with this. I got:
30, 29, 32. So my FC was 15 ~ 16 PPM.

That's unfortunately useless information.

I was as overly accurate as best I can. I even resorted to using a dropper and slowly dripping in while carefully watching the water level and tried to hit the 10 mm line exactly the same each time. Like down to the drop accuracy between tests.
The instructions say to use a heaping scoop of R-0870 and that the exact amount is not that important. However I got really particular about it and made sure I was heaping exact same sizes each time to try and eliminate variables.
When dropping in the R-0871 I made sure I held the bottle the same way each time, squeezed as consistently each time and dripped in about 1 drop per 1 second for the first 20 drops and then much slower after that working in 2 drops at a time till I could see the color fading out and then 1 drop at a time. I repeated over and over as you can tell and just cannot get consistent results. How are you supposed to test 1 PPM difference between day and night when I can't even do it back to back?

Is it just me or how are others getting this to work right? or is there something wrong with my kit?

Thanks for any feed back and help
Malcolm

 

[mknauss]

The 0871 bottle should be held vertical. Very little to no pressure on the bottle should be needed as the drops should form on the tip and fall naturally.

I suspect your drop size is variable.

 

[MalcolmV8]

The 0871 bottle should be held vertical. Very little to no pressure on the bottle should be needed as the drops should form on the tip and fall naturally.

I suspect your drop size is variable.

Yes I found upside down was the most consistent way I could get it and very minimal pressure. If it is indeed doing different size drops each time how do I fix that? or how do you get around that?

 

[mknauss]

To be honest, I just do the test and call it good. I would not obsess over it.

 

[MalcolmV8]

To be honest, I just do the test and call it good. I would not obsess over it.

I know what you mean but if the results are not repeatable then the data you're getting is not all that accurate. It puts you in the ball park which is good enough, but then again all these other kits I have also put me in the ball park and are also just ok. I specifically purchased the TF-100 because it was supposed to be accurate to 1 PPM on the chlorine test for the over night chlorine test at the end of the SLAM. I feel like that was a total waste.

 

[borjis]

I found that doing the oclt two days in a row was sufficient. That may be a workaround. I had mine pass on the second.

Never had to slam again after that.

 

[duraleigh]

You have testing errors. I cannot tell exactly what they are just yet but don't blame the FAS/DPD test. It is accurate to .2 ppm

There is no more accurate test on the market and if your pool water sample turns pink when you put in the powder, there is nothing wrong with the kit.
Describe for us the endpoint of the test......how do you know when the test is complete?

What compelled you to perform the test 8 times??? Sorry, I just HAVE to ask?

 

[ajw22]

Proper technique and drop size matters..

Water Testing Errors - Further Reading

www.troublefreepool.com

See..

and watch the way the bottle is held and the time it takes for a drop to form at 1:40 in...

 

[MalcolmV8]

You have testing errors. I cannot tell exactly what they are just yet but don't blame the FAS/DPD test. It is accurate to .2 ppm

There is no more accurate test on the market and if your pool water sample turns pink when you put in the powder, there is nothing wrong with the kit.
Describe for us the endpoint of the test......how do you know when the test is complete?

What compelled you to perform the test 8 times??? Sorry, I just HAVE to ask?

Obviously I was repeating the test over and over because I was unable to get consistent results. If you just run the test once and accept the results how do you know its repeatable with trying it again? If I had just blindly waited till the morning and run the test once more I would have compared those two results thinking they were accurate. They were not.

I don't see how the test is accurate to .2 ppm when I can't even get back to back tests to read within 3 ppm or so of each other. Granted I could be doing something wrong which is why I'm asking and explained my technics.

So I'm curious can you run the test twice and get the exact same result down to .2 ppm?

Proper technique and drop size matters..

Water Testing Errors - Further Reading

www.troublefreepool.com

See..

and watch the way the bottle is held and the time it takes for a drop to form at 1:40 in...

Thanks, I saw the instructions said to use a damp cloth or paper towel on the TA test I think it was. It did not explain why or why only on the TA test. That's something I could add in case static is messing it up. How accurate does the test come out for you? Thanks.

 

[duraleigh]

The static from the TA test is completely irrelevant to the FAS/DPD test.

The FAS/DPD test, when you use a 25ml water samp[le is accurate down to + or - one drop.......that's .2 ppm

Describe for us the endpoint of the test......how do you know when the test is complete?

 

[MalcolmV8]

The static from the TA test is completely irrelevant to the FAS/DPD test.

The FAS/DPD test, when you use a 25ml water samp[le is accurate down to + or - one drop.......that's .2 ppm

I was talking about the FAS/DPD chlorine test. Best I can tell that is supposed to be accurate to .5 ppm

The end point of the FC test is when the solution turns completely clear. Is that what you're asking?

 

[mguzzy]

What size sample were you using?...
5 ml sample is 1ppm accuracy and the multiplier is 1 x # of drops
10 ml sample is .5 ppm accuracy and the multiplier is .5 x # of drops
25 ml sample is .2 ppm accuracy and the multiplier is .2 x # of drops

I think I got that right.

 

[duraleigh]

mguzzy is correct. the FAS/DPD can be precise to within .2 ppm.

The end point of the FC test is when the solution turns completely clear. Is that what you're asking?

Not quite correct. You allow drops to fall off the dropper tip until the LAST drop you just added made NO FURTHER color change. Then you subtract that drop from the total and the remainder is the endpoint of your test.

 

[MalcolmV8]

What size sample were you using?...
5 ml sample is 1ppm accuracy and the multiplier is 1 x # of drops
10 ml sample is .5 ppm accuracy and the multiplier is .5 x # of drops
25 ml sample is .2 ppm accuracy and the multiplier is .2 x # of drops

I think I got that right.

I'm using the 10 ml sample as per the instructions.

mguzzy is correct. the FAS/DPD can be precise to within .2 ppm.

Not quite correct. You allow drops to fall off the dropper tip until the LAST drop you just added made NO FURTHER color change. Then you subtract that drop from the total and the remainder is the endpoint of your test.

That's a slightly different way of achieving the same thing. When it turns crystal clear I stop. Yes I can add one more drop to confirm crystal clear is crystal clear and subtract one but I only did that a few times because after it's completely clear no further changes happen. After doing the test multiple times you get used to the end. I had been doing multiple daily tests through the week so I had gotten pretty familiar with it. It wasn't till the end of the SLAM when I was going to do the over night CL lost test I decided to do back to back tests to make sure I was getting accurate results.

 

[mknauss]

Are you using a Speedstir device?

 

[duraleigh]

It is a TFP policy that no customer service is to be conducted on the forum. Where is my order? Why doesn't this work? My thingy is broke. Are all customer service items and this thread has reached that description and is being locked.

MalcolmV8, TFTestkits will be in touch and take care of your issue.