strange chlorine level behavior

[adridimo]

Hello, hope you can help understanding the following readings. Pool water a little bit cloudy, this is the first water test done yesterday evening:

05 Ago - 7:50 pm
FC 2.54
CC 0.26
TC 2.8
PH 7.2
ALKA 160 (i'm lowering it)
CYA 60
CH 218

I then added Liquid Clorine to increse the FC level to match my FC/CYA level and this where the readings:

05 Ago - 8.50 pm
FC 3.87
CC 1.18
TC 5.05
PH 7.2
ALKA 160 (i'm lowering it)
CYA 60
CH 218

How can be possible that after one hour the CC level began son high? Is that maybe that there was not enogh FC to combine with dirt?

After the last test I've decided to SLAM setting up the FC at 24ppm. This morning the water seems less cloudy.

Hope you can help me.

 

[mknauss]

You are expecting far more accuracy than your testing equipment can provide.

 

[adridimo]

You are expecting far more accuracy than your testing equipment can provide.

I'm not trying to handle a small difference in the readings, here we are talking of 5 times more the initial reading on CC.

 

[wireform]

Yes, once the chlorine starts to oxidize the CC will be more prevalent until it's gone.

 

[adridimo]

Yes, once the chlorine starts to oxidize the CC will be more prevalent until it's gone.

Thank you. So is a normal behavior. At the beginning there was not enoght FC to combine with the dirt?

 

[wireform]

If you were to test once without any chlorine present you'd see no CC also because as you said no chlorine no chloramine either.

 

[JamesW]

What test kit do you have?

You accuracy, precision and resolution are not as good as you think they are.

 

[adridimo]

What test kit do you have?

You accuracy, precision and resolution are not as good as you think they are.

I'm using a color meter Lovibond Scuba 3s, the precision and resolution specs seems good.. Next year I will buy the suggested test kit.

 

[JamesW]

I'm using a color meter Lovibond Scuba 3s, the precision and resolution specs seems good

I think that you are assuming a level of accuracy, precision and resolution that is not warranted.

You are reporting numbers to 1/100th of 1 ppm, which is 10 ppb.

This is not a realistic result.

The best you might get is +/- 0.2 ppm.

You assumption of accuracy, precision and resolution is probably off by a factor of at least 20.

 

[JamesW]

https://www.lovibond.com/ix_pim_assets/Wasseranalytik/Instruction_Manuals/Photometer/Scuba3s/00387976-1_scuba3s.pdf

Smart pool control with the Scuba3s electronic pool tester | Lovibond

Safety for the whole family: You have the most important 11 tests under control everywhere with data transmission via NFC and "result traffic light".

www.lovibond.com

 

[JamesW]

The manufacturer should provide the information about accuracy, precision and resolution.

However, these are under ideal conditions with perfect test conditions and perfect procedures with no interferences.

Realistically, you are not going to get better than +/- 0.2 ppm accuracy, precision and/or resolution.

Sensitivity is an absolute quantity, the smallest absolute amount of change that can be detected by a measurement.

Accuracy can be defined as the amount of uncertainty in a measurement with respect to an absolute standard.
Accuracy is an indication of the correctness of a measurement.

The resolution of a measurement system is the smallest yet to distinguish different in values.

Precision describes the reproducibility of the measurement.
The term precision is used to express the random measurement error.

Accuracy refers to how close measurements are to the true or accepted value. It’s the degree to which the result of a measurement reflects the actual value of the quantity being measured. Accuracy reflects the absence of error, both systematic and observational, in your measurement system.

Precision, on the other hand, is about the repeatability or consistency of measurements. It answers the question, “how close are measurements to each other?” Precision can exist without true accuracy; you can have measurements that are very consistent but still far from the known or accepted value.

Resolution in metrology equipment dictates the smallest change in a physical quantity that a measurement system can detect. It plays a pivotal role in determining both precision and accuracy, as higher resolution allows for finer distinctions in measurements.

https://www.lovibond.com/ix_pim_assets/Wasseranalytik/BookOfMethods_Publication/Einzelmethode/M100/Instruction_Manual_Single_Method_-_M100_-_Chlorine_T_-_en.pdf

Free and Total Chlorine Portable Photometer - H I97 71

The HI97711 Free and Total Chlorine Photometer combines accuracy and ease of use in a simple, portable design to measure free and total chlorine in water samples from 0.00 to 5.00 mg/L (ppm).

www.hannainst.com

https://www.hannainst.com/hubfs/product-manuals/MAN97711_12_19.pdf

 

[n0rthern]

I think that you are assuming a level of accuracy, precision and resolution that is not warranted.

You are reporting numbers to 1/100th of 1 ppm, which is 10 ppb.

This is not a realistic result.

The best you might get is +/- 0.2 ppm.

You assumption of accuracy, precision and resolution is probably off by a factor of at least 20.

I use the same Lovibond tablet reagents. The attached picture details their accuracy over the test range using the SCUBA2 photometer (previous model). And I already know that the USA/TFP and Europe/TFP crews disagree over photometers. Do not want to open up that debate again.

 

[JamesW]

FC 3.87
CC 1.18
TC 5.05

FC 2.54
CC 0.26
TC 2.8

Assuming a +/- of 0.5, the results are not significant.

 

[adridimo]

@JamesW so my testing method is not useful when appling the TFP methodology?

I've contacted the TFTestKit and we are organizing the shipping to Italy of a TF-PRO SALT kit hoping this would be helpful.

 

[JamesW]

My main point is that you have to understand the limits of the tests.

Most likely, the CC levels can be ignored as long as you are maintaining the correct chlorine level for your cyanuric acid level and you pass an OCLT.

Overnight Chlorine Loss Test

 

[adridimo]

My main point is that you have to understand the limits of the tests.

Most likely, the CC levels can be ignored as long as you are maintaining the correct chlorine level for your cyanuric acid level and you pass an OCLT.

Overnight Chlorine Loss Test

I understand the limit as every measuring instrument got it. My big problem now is that my instrument is not able to detect FC over 6PPM and with my level of FC/CYA a need an other instrument. Let's see if the TFK test will ship it soon to Italy.

At the moment i'm try to slam in "open loop" or "without feedback". Starting from a detectable FC I increse my FC only calculating the quantity of liquid clorine needed. Till now it worked:
- pool finish build and opened on 14/07/2024
- cloudy water on 5/07/2024
- SLAM on 5/07/2024
- Today 07/07/2024 crystal clear water.

I'll check the OCLT when FC will go down to detactable value waiting the TFK test.

By the way, if my actual instrument has a range for FC from 0ppm to 6ppm. If a diluite the pool water by 1:2 with tap water, can I detect a bigger range with a certain error?

 

[JamesW]

If a dilute the pool water by 1:2 with tap water, can I detect a bigger range with a certain error?

If you use distilled water, that should work well enough.

Pool Water........Distilled Water.....Multiply by

..........1...........................1...............................2
..........1...........................2...............................3
..........1...........................3...............................4

 

[mknauss]

If a diluite the pool water by 1:2 with tap water, can I detect a bigger range with a certain error?

Distilled water. Most tap water has chlorine/chloramines in it.

You error will quadruple.

 

[JamesW]

Pool Care Basics

Overnight Chlorine Loss Test

SLAM Process

PoolMath

FC/CYA Levels

Test Kits Compared

 

[adridimo]

If you use distilled water, that should work well enough.

Pool Water........Distilled Water.....Multiply by

..........1...........................1...............................2
..........1...........................2...............................3
..........1...........................3...............................4

I'll use distilled water and try! thank you again!!!