CYA not considered in Pool Math?

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Dissolved oxygen can react with the DPD reagent, causing a color change even if no chlorine is present, especially in high-oxygen conditions or when testing for very low chlorine levels.

Both Standard Methods and ISO procedures call for liquid DPD reagents prepared from DPD sulfate or DPD oxalate salts.

Liquid DPD reagents, inherently unstable, are subject to oxidation from either atmospheric oxygen or dissolved oxygen present in the preparation water.

It has been shown that the oxidation of DPD by oxygen is pH–dependent (Ref.2.5).

The liquid DPD formulations attempt to retard oxidation by lowering the pH of the indicator reagent.

The liquid formulations also incorporate disodium ethylenediamine tetraacetate (Na2EDTA) in order to “retard deterioration due to oxidation and, in the test itself, provide suppression of dissolved oxygen errors by preventing trace metal catalysis” (Ref 2.6).

The practice of adding Na2EDTA to the DPD indicator reagent is questionable because of the low solubility of EDTA in dilute acid solutions.

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JoyfulNoise said:
One other aspect of the test is that the DPD dye can be oxidized by air and turn pink. It doesn't typically happen because most pool water is fairly low in dissolved oxygen, but an extensive resting period after adding the dye could cause an slight increase in the titrant consumption.
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Free Cl2 reacts with the DPD color indicator, in the presence of phosphate buffer, to form a red dye.

Interferences.

Additional halogens and halogenating agents produce positive interferences.

Oxidized manganese and ozone are positive interferences.

Color and suspended matter may interfere with the photometric measurement.

Chlorine greater than 500 mg/L will oxidize the DPD to a colorless amine, which can be interpreted as a low chlorine value.

High pH levels cause dissolved oxygen to react with the reagents.

Very low pH causes a positive free chlorine residual when mono-chloramines are present.

The test should be conducted between 20 and 25 °C.
 
DougJack said:
I really agree with that point of view. I find it a useful tool that is helpful to me to find some but not all, critical elements of an approach, even if I think I know a subject well. I almost always find a flaw if I question more deeply as above. But its response often contains a hint of what will become important in my next set of questions.
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Sometimes yea. I ran a test of an AI tool that (still) claims it can tell the difference between a genuine photo and a manipulated photo and was able to fool it quite easily. The AI can make pretty pictures though.
 
DougJack said:
I have considered big dilutions to be able to measure strength
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You need to dilute the bleach by 10,000 to 1 and then test the diluted bleach.

You can do 0.1 ml of 10% to 1 liter of water for 10 ppm. But .1ml is really hard to measure.

One way to do the dilution is to add 10 ml of bleach to 1 liter of water, mix thoroughly, then add 10 ml of that to another liter of water, mix thoroughly and then test the FC level. The two liters of water need to be chlorine free, commonly distilled water is used. Also, the 10 ml measurement needs to be as accurate as possible, typically done using a syringe or pipette.

Then you can use effects of adding, enter 1 liter for pool volume, liquid chlorine, and .1milliters for the LC amount. Change the percent until it matches your test result.
 
ajw22 said:
No emotion involved by me on you opinion shopping between real people and robots.

When you run out of your own thoughts you turn to robots and bring it here.

Explain what YOU do not understand about what has been explained you. Not what you imagine happens.
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Sure - no one has explained the dynamics of adding FC. Simplistically if the Total bonded and unbonded chlorine is what is being measured, and I want to double the FC measured, and there is 20x more bonded than unbonded then I need to double the total. When I pour in the chlorine that pool math seems to recommend it only recommends to add what is needed for FC unbonded. As time goes by the system goes to equilibrium and 95% of the added chlorine becomes bound and the FC must drop after addition and without any consumption. Eventually with no consumption the other 95% of chlorine needs to be added to actually have the target unbonded free chlorine. The dynamics that I am interested in is how long does the binding process to reach the new equilibrium point.
 
PoolStored said:
You need to dilute the bleach by 10,000 to 1 and then test the diluted bleach.

You can do 0.1 ml of 10% to 1 liter of water for 10 ppm. But .1ml is really hard to measure.

One way to do the dilution is to add 10 ml of bleach to 1 liter of water, mix thoroughly, then add 10 ml of that to another liter of water, mix thoroughly and then test the FC level. The two liters of water need to be chlorine free, commonly distilled water is used. Also, the 10 ml measurement needs to be as accurate as possible, typically done using a syringe or pipette.

Then you can use effects of adding, enter 1 liter for pool volume, liquid chlorine, and .1milliters for the LC amount. Change the percent until it matches your test result.
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Great - it's going to be near the top of my list when I get back.
 
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First Acid Ionization Constant of the Drinking Water Relevant Chemical Cyanuric Acid from 5 to 35 °C - PMC

Cyanuric acid is present in drinking water when chemicals commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) or trichlor (trichloroisocyanuric acid) are used as alternative free chlorine ...
pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov

Chlorinated Cyanurates: Review of Water Chemistry and Associated Drinking Water Implications - PMC

Since 1958, cyanuric acid and two chlorinated cyanurates, commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) or trichlor (trichloroisocyanuric acid), have been added to outdoor swimming ...
pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov

blog.orendatech.com

Chlorine, pH and Cyanuric Acid Relationships

pH controls chlorine strength (% HOCl), but NOT when Cyanuric Acid (CYA) is in the pool. CYA takes over control of chlorine strength. Did you know that? Chlorine and cyanuric acid.
blog.orendatech.com blog.orendatech.com


 
Have you tested FC, added LC and tested again to see if you reached your target FC? I use this method to back into a percentage for LC. Effects of adding, change the percentage until you see your ride form the addition.
 
ajw22 said:
No emotion involved by me on you opinion shopping between real people and robots.

When you run out of your own thoughts you turn to robots and bring it here.

Explain what YOU do not understand about what has been explained you. Not what you imagine happens.
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So - I finally got it. I kept thinking that the DPD measurement was not measuring all FC + iso cyanurates. I see now that the measurement essentially removes the bonded HOCL and sees the FC as if the CYA wasn't there. So there is no need to make an adjustment in dosage to compensate for the CYA because there is no impact in that measurement from CYA. Lilrly my liquid chlorine is degrade by the extra percentage I have to add....
 
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DougJack said:
So - I finally got it. I kept thinking that the DPD measurement was not measuring all FC + iso cyanurates. I see now that the measurement essentially removes the bonded HOCL and sees the FC as if the CYA wasn't there. So there is no need to make an adjustment in dosage to compensate for the CYA because there is no impact in that measurement from CYA. Lilrly my liquid chlorine is degrade by the extra percentage I have to add....
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I do believe that was what we said back in the beginning. And the reaction or release times are very fast, less then a second.

Furthermore, Jensen and Johnson (1990) used stopped-flow spectroscopy to determine that a chlorinated cyanuric solution and a free chlorine only solution had the same t1/2 (0.4 seconds) when reacting with DPD, suggesting an extremely fast release of HOCl from chlorinated cyanurates.
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