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Dichlor/bleach Method In A Nutshell


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How big is your tub and how are you testing? There is a known interference with phenol red used to test pH and high sanitizer levels. 3 to 4 Tbls. of 7.5% bleach will raise 100 gal. 9 to 12 ppm over the starting point (usually around 3 to 5 ppm) and pH test will show this interference when sanitizer is over 5 to 10 ppm, depending on who makes the reagent. The effect of the interference in that the pH will read high when it is not. Your pH is not rising, it's still 7.4 and my guess is that you free chlorine is high when you get the high pH reading

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my tub is 375 gallons.  I am testing with a taylor.  Everything your saying makes sense, except my sanitizer never tests very high.  If I put a couple tbs of muriatic acid in, my ph tests 7.4.  Next day the PH tests over 8 again.  Only thing I am adding is Bleach, so that is why I am thinking the bleach is the cause.  Thank you for the time and knowledge.  It's a bit frustrating when you have all your numbers right where you want them and then only one goes crazy on ya.

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On 7/8/2022 at 8:51 AM, RHeller1 said:

I am testing with a taylor. 

Which kit?
All the DPD based kits such as the K-2005 can bleach out at high sanitizer levels (unless you dilute the sample and make the appropriate calculations on the reading) leaving you to believe that the sanitizer is much lower than it really is. The only kit that is immune to this until sanitizer gets to extremely high levels is their FSD-DPD testing method found in the K-2006/2106 kits and as a standalone kit. OTO testing (which only tests total chlorine) will also be immune to bleachout from high sanitizer.

Performance bleach is fine and will not cause the pH rise you are seeing.


Based on what you have said so far the most logical explanation is that you are testing with DPD, your sanitizer is much higher than you think causing a partial bleachout of the DPD which leads you to think your sanitizer is low when it is actually high. The high sanitizer is causing the phenol red indicator to convert to chlorophenol red which has the same color changes as phenol red but test a pH range of  4.8 to 6.7 so when the pH indicates that it's 8.0 all you really know is that it's greater than or equal to 6.7 and when you add the acid you are bringing the pH below 6.7 so you are getting a different pH reading that is equivalent to the 7.4 but is much lower.

If you are using FAS-DPD testing then a full set of test results might give us more information.

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I am using the k-2006

So since my first post, I have quit using the clorox performance bleach and went with liquid pool chlorine.  

My PH has read 7.6 the last 2 days, my TA is at 60, my CYA is at 38 and my chlorine is at 4ppm.  I cant explain this, but something in my tub does not like performance bleach

 

 

 

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15 hours ago, RHeller1 said:

my CYA is at 38

This reading is impossible to achieve with a Taylor K-2006. The test has a precision of +/- 10 ppm and the scale is logarithmic so you cannot interpolate readings between the marked ones on the CYA test tube. Are you using a 10 ml or 25 ml sample for the chlorine tests? Is your 4 ppm reading for chlorine Free chlorine or Combined Chlorine? Are you using MPS?

The only thing different about performance bleach is the inclusion of Poly(Diallyldimethylammonium Chloride) and Polyacrylic Acid, which are common ingredients in many pool clarifiers. They are coagulants that cause small particles to clump together that, in laundry, prevent dirt from redepositing back on clothes and in pools and spas, cause them to become large enough to be filtered out by the filter. neither would have an adverse affect on pH. All other ingredients in performance bleach besides the sodium hypochlorite, are also found in pool chlorine and other liquid sodium hypochlorite products, either as breakdown products as the bleach weakens with time or for manufacturing and stabilizing (sodium chloride (salt), water, sodium hydroxide, sodium chlorate, sodium carbonate).

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ok, say 40, but it was right past the 40 line for CYA.  I am using a 25ml for my chlorine test.  I use MPS once a month.  I understand pool chlorine and bleach are basically the same, thats what is bugging me.  

 

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13 hours ago, RHeller1 said:

I am using a 25ml for my chlorine test.

no need for that much precision (.2 ppm is overkill and can lead to error because of the number of drops to count.)

 

Use the 10 ml sample, 1 scoop of DPD powder and then each drop will be equivalent to .5 ppm FC. Add 5 drops of DPD reagent 3 for the CC test and then each drop will be .5 ppm combined chlorine. You want to shock or add MPS when the CC is persistant and greater than .5 ppm (> or = 1 ppm). If you are using MPS then you need to get the R-0867 Deox Reagent to remove the interference (MPS will test as combined chlorine). The 2 oz. kit

https://taylortechnologies.com/en/uproduct/reagent-pack-monopersulfate-interference-remover-for-2000-series-kits-w-2-oz-re?id=K-2042

is a better bargain than the .75 oz kit

https://taylortechnologies.com/en/product/test-kits/reagent-packmonopersulfate-interference-remover-for-2000-series-kits-w-75oz-rea--K-2041

but it won't fit in your plastic case.

 

On 7/8/2022 at 8:51 AM, RHeller1 said:

Next day the PH tests over 8 again.

Just noticed this rereading the posts. What is your TA? (or what was it when you were having the pH problem?)

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