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Thread: Help with Hot Tub chemicals

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    Post Help with Hot Tub chemicals

    I just ordered my Taylor kit last week and used it tonight. I cleaned and refilled my 350 gallon hot tub, added sanitizing granules (4 tsp) and tested it 10 hours later.

    These are the results

    FC: 11
    TA: 140
    PH: 8

    Since the FC level is so high, does that effect the TA and PH, causing them to be high? What's the best way to get these numbers down? I have some PH - on hand.

    Any help is appreciated! I am getting so frustrated with trying to manage these chemicals

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    Mod Squad tim5055's Avatar
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    Re: Help with Hot Tub chemicals

    Chlorine above 15 may mess up pH readings using the Taylor kit, so your numbers are probably good.

    Read through How do I use Chlorine in my Spa as it explains how to balance the TA/pH.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: Help with Hot Tub chemicals

    I actually believe above 10 is where the PH readings start becoming inaccurate. Here's one of many

    Quote Originally Posted by UnderWaterVanya View Post
    Actually if FC is 10+, pH will measure high even when it really is not. Let the FC drop below 10 before checking pH any further.
    12500 gallons, 24 foot round above ground
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    Re: Help with Hot Tub chemicals

    Thanks. I'll test it again after having cover open and hopefully the FC will be down some.

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    Mod Squad tim5055's Avatar
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    Re: Help with Hot Tub chemicals

    Quote Originally Posted by scott.MI View Post
    I actually believe above 10 is where the PH readings start becoming inaccurate.
    While I have seen many folks quote the 10 limit (including ChemGeek who I trust with his information), this is posted on the Pool School Definitions and Abbreviations Page (bold/red mine) under "pH Potential of Hydrogen"

    A measure of how acidic or basic (alkaline) a solution is. A pH of 7 is considered neutral, anything above 7 is basic and anything below is acidic. Pools are usually kept at a pH from 7.2 to 7.8. pH in pools is tested with the indicator phenol red. High sanitizer levels above about 5 ppm can interfere with this test and lead you to believe that your pH is very high when it is actually not! The better test kits will allow for this by adding a chlorine neutralizer to the indicator and calibrating their color comparator blocks to compensate for the added chlorine neutralizer so you can get accurate pH readings when your sanitizer levels are at 10-15 ppm.
    Maybe this page needs to be changed from 10 - 15 to just 10? If so I may need to adjust my testing methods as I need to keep my FC above 10 due to my high CYA.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: Help with Hot Tub chemicals

    Technically if you measure the pH quickly then the absolute FC limit is not that relevant since it is the active chlorine level that oxidizes the pH reagent to give it a false color. So when CYA is in the water, the pH will probably measure correctly at first and then drift up to the false purple color. We don't confuse things in the Pool School with this kind of info because "it depends". It's just simpler to give the rule as stated. 10 ppm FC is not a hard and fast number. It really depends on the CYA level so depends if you are at normal levels or shock levels, for example.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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