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Thread: Celebrate or start pouring...pH readings from different kits

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    Celebrate or start pouring...pH readings from different kits

    I have three different test kits that measure pH (among other things) and I get readings that vary from 7.2 up to 8.2 depending on which kit I use. The readings are consistant within a kit, but I don't know if I should start adding HCl or celebrate for having prestine pH levels (all other levels look good except for too much CYA, or should I not believe it....)
    Two kits use a stick test, one uses the drops in solution. I am thinking of buying the kit that TFP recommends...is there a standard out there that is true and tested and/or is there somebody who has verified any of kits? Is across the board readings typical for different kits? And yes, the kits are in a cool, dark place, not expired.
    Spa Geek
    500 gallon outdoor above-ground 8'x8' acrylic hot tub

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    Mod Squad zea3's Avatar
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    Re: Celebrate or start pouring...pH readings from different

    The drop based kits are going to be more accurate than test strips.
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    Re: Celebrate or start pouring...pH readings from different

    Drops every time over strips.

    Scott
    Owner of - PoolGuyNJ LLC
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    Re: Celebrate or start pouring...pH readings from different

    You might be having funny Ph readings due to a false alkalinity reading. Its very odd that each kit tests differently though. This may suggest one of the is bad.

    Remember that CYA levels above 60 need a 1/3 of the value subtracted from your Total Alkalinity.
    e.g. 100 cya, 100 Total Alkalinity - 33 = 67 "true" alkalinity
    This tends to lead to a PH that SEEMS like its always on the money and you'll hear things like "I never add Acid to my pool." If you have an InGround hard wall pool and you never add acid, something is probably wrong.

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    Re: Celebrate or start pouring...pH readings from different

    Hi, Carl,

    Ditch the strips forever!

    If your reagent is fresh and the FC is not in excess of 10ppm, you can normally count on drops based pH tests to be quite accurate.
    Dave S.
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    Re: Celebrate or start pouring...pH readings from different

    Quote Originally Posted by ProPoolGuy
    Remember that CYA levels above 60 need a 1/3 of the value subtracted from your Total Alkalinity.
    e.g. 100 cya, 100 Total Alkalinity - 33 = 67 "true" alkalinity
    This tends to lead to a PH that SEEMS like its always on the money and you'll hear things like "I never add Acid to my pool." If you have an InGround hard wall pool and you never add acid, something is probably wrong.
    The TA adjustment for the CYA level is only useful when calculating carbonate alkalinity, which is really only used for LSI calculations (and handled automatically by the Pool Calculator). The number you want, and the one we always use here, is the TA result straight from the test kit.

    It is very possible for PH to be stable in a plaster pool after the first year. PH tests can also be thrown off by high FC levels. All PH test kits are affected by the FC level, but some are more affected than others. The Taylor chemistry based kits work well with FC up to 10 and are usable when FC is up to 15. Some of the cheaper PH tests start having problems at FC levels as low as 5. It is also possible, but not as likely, for the PH test reagent to go bad. Usually the PH reagent will stain the bottle when it goes bad. If the plastic is staining then the reagent is bad. If the plastic is not staining, then you can't tell for sure.
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