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Thread: Pool Opening - Amount of Chlorine Needed to Shock

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    Pool Opening - Amount of Chlorine Needed to Shock

    Hey All,

    I probably won't open my pool until the 3rd week in May and will be adding some bleach in the water until then, since the outside temps are getting warmer, but my question is this:

    When I do open, based on my CYA level (~50) it says I should be shocking to '15' which is almost 933oz. of bleach - isn't that excessive? In the past, I've opened the pool to find a lot of green algae, primarily because it got warm and I have a mesh cover, and have added about 6 1lb. bags of shock. I'd prefer to use just straight Chlorox this year, but am struggling finding out how much I should really add, despite having algae or not. Any suggestions?

    And, do I also need to add algaecide or not when opening since I added it when I closed the pool?

    I'm just trying to get all my ducks in a row and make sure I have all of the proper chemicals before opening time rolls around.

    My understanding is to 1) adjust pH & CYA levels then 2) shock.

    Thanks,
    Z
    30k gallon salt water pool, Jandy Stealth 2.5HP pump, Jandy CL460 cartridge filter, Jandy AquaPure 1400 SWG, Jandy Lite 400k BTU heater, Polaris 360

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    JasonLion's Avatar
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    Re: Pool Opening - Amount of Chlorine Needed to Shock

    It appears you have done your calculations correctly. 6 lbs of 65% cal-hypo will raise FC by close to 15 in 30,000 gallons. 933 oz of ordinary 6% bleach will also raise FC by close to 15 in 30,000. It does take much more volume of bleach to have the same effect as the powdered/granular forms chlorine.

    There isn't really any point in using algaecide when opening. Algaecide is most effective at preventing algae, and not very useful when you already have algae. That is the main reason why you use it when closing, but not when opening.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Pool Opening - Amount of Chlorine Needed to Shock

    Makes sense, the bleach is still cheaper but raises the pH a bit...I'm not sure what I'll go with, just making sure my logic was correct. Thanks for your help.
    30k gallon salt water pool, Jandy Stealth 2.5HP pump, Jandy CL460 cartridge filter, Jandy AquaPure 1400 SWG, Jandy Lite 400k BTU heater, Polaris 360

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    Mod Squad jblizzle's Avatar
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    Re: Pool Opening - Amount of Chlorine Needed to Shock

    I was under the impression that bleach had little long term affect on the Ph. It may go up initially but then drops back down as the bleach is "processed ".
    Jason, TFP Moderator
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    Re: Pool Opening - Amount of Chlorine Needed to Shock

    Most importantly, you may need that dose as calculated for the first dose, but then you need to retest the FC and keep the level up in the hours after the first dose circulates and gets used up against the algae.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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