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Thread: How exact do you have to be with water tests?

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    phalcon51's Avatar
    Join Date
    Oct 2010
    So. California

    How exact do you have to be with water tests?

    I'm pretty finicky about doing my water tests; I use exactly the number of drops called for, hold the bottle vertically instead of at an angle and generally follow the instructions to a "T". I occasionally take a water sample to my local Leslie's just to see how well their results agree with mine. Of the three employees that work there on different days all three have a different way of doing the tests. The worst one typically overfills the sample vials, puts in 8 or 9 drops of reagent when it calls for five, shakes the sample to mix instead of inverting, etc. Just wondering how sensitive these tests are to following the instructions exactly vs. just getting it sorta close. What's your experience?

    26,200 gal. 35' x 16' Plaster IGP (50 yrs. old), Hayward 48 sq. ft. DE filter, Hayward EcoStar VS pump, Intellichlor IC-40 SWCG, The Pool Cleaner 4X suction, Pool Skim and Pool Devil skimmers. Re-plastered Sept. 2010.

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    Mod Squad JohnT's Avatar
    Join Date
    Apr 2007
    SW Indiana

    Re: How exact do you have to be with water tests?

    Some can be pretty touchy. Not holding the bottles vertically can lead to variation in drop size, and missing the mark on the vial can change the concentration as well. Most measurements of any kind are the worst when you combine errors such as small drop size and an overfilled vial.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

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    JesseJames's Avatar
    Join Date
    Sep 2009

    Re: How exact do you have to be with water tests?

    I gave up on the pool store tests. Around here the employees are mostly college kids who couldn't care less about my swimming pool. I decided it was a waste of time.
    13K Gal., Plaster, SWG, Intellichlor IC 20, Sta-Rite 1 HP Pump, Sta-Rite PLM 300 Filter, Pentair LED, Solar, Screened Enclosure, Great White, TF-100

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    Mod Squad Bama Rambler's Avatar
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    Jun 2009
    SouthWest Alabama

    Re: How exact do you have to be with water tests?

    Accurate testing is one of the major tenants of this site. I, like you make sure I do the tests as accurately as possible. I figure there's enough inaccuracy in the tests themselves that I don't need to be adding any due to my sloppiness.

    By the way, I've noticed the same thing at the local pool stores around here to. They just don't seem to get it.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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    benavidescj's Avatar
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    Apr 2010
    Fleming Island, FL

    Re: How exact do you have to be with water tests?

    I don't see the point in doing the test if not done correctly. If done incorrectly you will get a result and may even take action based on that result which in itself might be inaccurate. I too do it accurately because I want to know exactly what I have. I am anal though and love my pool.
    Pool: 28,000 gallons IG; IC 40 SWG; Pentair 120 gpm cartridge filter; Marble finish; Pentair Wisperflow 1.5 hp; Polaris 360
    Spa: 350 gallon; Bromine
    How to shock your pool

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: How exact do you have to be with water tests?

    With a little attention it is easy to do the tests the way they were designed to be done, which will keep your errors under 10% (for the most part). When you are more casual about things like filling the vial too high or adding the wrong number of drops it is easy for errors to mount to over 40%, and possibly much more, depending on what you actually did. At that point you risk having a wide range of problems and losing control over your chemistry.

    Many of the methods we teach here depend on maintaining reasonable accuracy/precision in your test results. Some errors are unavoidable and some of the tests are less precise than others. We try to take those issues into account in our recommendations. But when you start adding other mistakes on top of the inherent challenges, things can easily go beyond acceptable limits and cause problems.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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