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Thread: Startup Question

  1. Back To Top    #1

    Join Date
    Jul 2009
    Location
    Port Orchard, WA
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    16

    Startup Question

    I filled my tub and checked the chemistry before heating or adding anything. My pH was 7.2 and TA was 60. After filling and heating, I added 2 cups bleach per pool calculator. I just checked tonight and of course the chlorine is really high but the pH shot through the roof! It's like 8.4 or higher. Is it normal for high chlorine level to raise the pH high also? I put a little dry acid in to lower it, but I'm wondering, does it go down as you use up chlorine?
    500 gal. Arctic Summit Legend Extreme Spa with Onzen SWG & Micropure Silver Sentinel micron disposable filter

  2. Back To Top    #2

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
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    12,082

    Re: Startup Question

    Adding 2 cups of 6% bleach in 500 gallons would raise the FC by 15.4 ppm. Are you trying to decontaminate your spa or did you want the FC to be that high? With your numbers, the bleach would have the pH rise to around 7.7. Don't forget that high FC levels above 10 ppm can lead to a falsely high pH reading as the high chlorine level bleaches out one of the two indicators in the pH test. The pH will come down some as the FC drops. When the FC is closer to 5 ppm or so, check the pH.

    If you are using the Dichlor-then-bleach method, then using 50 ppm Borates is recommended (after your TA is low enough to have reasonably stable pH) as this will help to stabilize the pH further, reducing the fluctuation in pH when bleach is added and then consumed.

    Also, note that Clorox 6% regular unscented bleach has the least amount of excess lye in it, but if you are using an off-brand Ultra bleach (or an off-brand regular bleach, though that is really weak at 3% or less) then they usually have a lot more excess lye in them so generally aren't as good to use unless you don't mind adding acid to compensate for the rise in pH.

    Finally, you will probably have a stable pH target in the 7.5 to 7.7 range -- unlikely to be much below 7.5 so don't try to fight it.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  3. Back To Top    #3

    Join Date
    Jul 2009
    Location
    Port Orchard, WA
    Posts
    16

    Re: Startup Question

    Quote Originally Posted by chem geek
    Adding 2 cups of 6% bleach in 500 gallons would raise the FC by 15.4 ppm. Are you trying to decontaminate your spa or did you want the FC to be that high?
    I thought I read that when you first start up following a fresh refill,you should basically shock it. I guess I'm incorrect there?
    500 gal. Arctic Summit Legend Extreme Spa with Onzen SWG & Micropure Silver Sentinel micron disposable filter

  4. Back To Top    #4

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: Startup Question

    Well, it's probably an OK idea unless the water is changed fairly quickly (i.e. you drain and refill in the same day). A more serious decontamination is needed when the spa is new or if it's been sitting without chlorine for a while, but a drain/refill probably doesn't have to have a shock to start out unless the fill water isn't particularly clean for some reason. Basically, shocking won't hurt, but may not be needed.

    I would say that if after a fresh refill the chlorine demand doesn't seem to be unusually high, then shocking isn't needed.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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