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Thread: Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

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    Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

    I notice the 9056 DPD comparator goes to 10 after many years of being limited to 5. Taylor made a big deal in their blurbs for the new extended range comparator about how great it is. So I was wondering if there is any technical reason why Taylor couldn't do the same for the OTO comparator. Searching the forums and indeed the whole Internet I couldn't find any technical reason for the current limit so I'm thinking it is just market driven.
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    Mod Squad jblizzle's Avatar
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    Re: Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

    The shades of yellow are already very hard to distinguish adding more shades would be doubtful to help

    There is a "loose" scale posted around here somewhere. Where the shade starts to get deep yellow, then orange, then deep orange, etc
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    JoyfulNoise's Avatar
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    Re: Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

    Just order the 9056 comparator and the R-0001/R-0002 reagents. Or purchase a K-1001 kit or K-1004 and add a 9056 comparator to it. Much more accurate than OTO and you can actually titrate the resulting pink solution to a clear endpoint using the R-0871 drops just as if you used the powder (R-0870). The precision is roughly 0.5ppm/drop.

    OTO is simply inaccurate above 5ppm. It is not a quantitative test and should never be used that way.


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    Re: Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

    Quote Originally Posted by JoyfulNoise View Post
    OTO is simply inaccurate above 5ppm. It is not a quantitative test and should never be used that way.
    There's no comparator to read above 5 ppm! I wouldn't expect accuracy without a proper comparator.

    Maybe there's a technical limitation in the chemistry but if there is I haven't seen that described anywhere. Hence the question on the table.
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    JoyfulNoise's Avatar
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    Re: Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

    See Page 8 - https://www.hach.com/cms-portals/hac...neAnalysis.pdf

    2e. Other Common Analytical Methods
    Orthotolidine Method
    The orthotolidine (OT) method for chlorine was first reported by Ellms and Hauser (Ref. 2.14). The method has been modified several times to overcome stability problems and interferences related to monochloramine breakthrough in the free chlorine procedure.
    The orthotolidine method was dropped from the 14th edition of Standard Methods after the results of two round-robin studies (Refs. 2.15, 2.16) were released. Both studies indicated the OT method gave poor accuracy and precision and a high overall error in comparison with the other chlorine methods.
    Two aquatic toxicity studies (Refs. 2.17, 2.18) compared the DPD colorimetric, amperometric titration and orthotolidine methods for determining chlorine residuals. In both studies, the OT method gave lower values at all concentrations of total chlorine relative to the other two methods.
    Because of relatively poor accuracy and precision and a lack of specificity, the orthotolidine method generally is not accepted in the United States and most developed countries. Usage of this method is mainly confined to low-cost pool testing applications.
    The method is simply inaccurate and has low specificity (i.e., color distinctions) and so making a comparator up to 10ppm would be pointless because the value is meaningless. OTO is simply not QUANTITATIVE - even at lower chlorine levels you can't say that a 5ppm yellow color is actually 5ppm. This is the very reason why I stopped using OTO all together. I could have total chlorine levels anywhere from 2 to 8ppm (as measured by FAS-DPD) and the yellow color was always the same shade. It's really a useless test.


    Matt
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    Re: Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

    I asked Taylor why they stop at 5ppm. They said current industry recommendations for FC in residential pools is 2-4 ppm with a max of 5ppm. So as i suspected they are just following the market. Nothing more complicated than that.
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    Re: Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

    Quote Originally Posted by Poolzzz View Post
    I asked Taylor why they stop at 5ppm. They said current industry recommendations for FC in residential pools is 2-4 ppm with a max of 5ppm. So as i suspected they are just following the market. Nothing more complicated than that.
    Hmm, that's an interesting response considering that Taylor also makes the reagents for the FAS / DPD test that can very accurately measure FC up to 50ppm. While that test is aimed at commercial pool services, there is nothing that states it is not to be used commercially in a residential pool.

    I think that whoever you spoke to simply told you what they believed you wanted to hear......
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    Re: Any technical reason OTO chlorine test limited to 5 versus 10 ppm?

    Quote Originally Posted by domct203 View Post
    Hmm, that's an interesting response considering that Taylor also makes the reagents for the FAS / DPD test that can very accurately measure FC up to 50ppm. While that test is aimed at commercial pool services, there is nothing that states it is not to be used commercially in a residential pool.
    Yes, they said that too. The commercial market is driven by public health standards which currently has a maximum of 10 ppm. It's all based on the standards of intended market.
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    Cartridge Filter, 530 gph Intex pump
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    TF 100 Test Kit w/SpeedStir

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