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Thread: Does pool shocking work more slowly in cold weather?

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    Does pool shocking work more slowly in cold weather?

    I have been busy and let my pool go. It got lots of leaves in. When I finally got around to cleaning it, the water was green. It goes down to freezing here at night, then gets into the 40's in the day, so the water is pretty cold. I shocked it last night with what I calculated was the proper amount of bleach, but this morning the water is still green. Maybe I miscalculated something, but before I add more bleach, I would like to know if shocking works differently in cold water.
    36 x 18 oval pool, inground, plaster pool.
    27000 gallons
    1 hp pump. Sand filter
    Pool built in 1971.

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    Mod Squad jblizzle's Avatar
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    Re: Does pool shocking work more slowly in cold weather?

    We do not shock our pools here at TFP. If you have algae, you need to follow the ShockLevelAndMAINTAIN Process

    This is not a one time chlorine addition as it appears that you have done. This process actually goes a little faster in colder water due to lower losses to the sun and the algae can not grow as fast.
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    Re: Does pool shocking work more slowly in cold weather?

    Thanks.
    36 x 18 oval pool, inground, plaster pool.
    27000 gallons
    1 hp pump. Sand filter
    Pool built in 1971.

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    Re: Does pool shocking work more slowly in cold weather?

    This is sort of a related question so I'll ask here rather than starting a new thread.

    Do you know if it effects the power of liquid bleach if it is kept in an unheated garage where it freezes and thaws, freezes and thaws, throughout the winter?
    36 x 18 oval pool, inground, plaster pool.
    27000 gallons
    1 hp pump. Sand filter
    Pool built in 1971.

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    San Rafael, CA USA
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    Re: Does pool shocking work more slowly in cold weather?

    While there is less chlorine loss at lower temperature and with the sun lower in the sky (or being overcast) and algae growth is much slower, all chemical reactions (including those involving chlorine) slow down at colder temperatures. At 40F such reactions will be around 8 times slower than at 80F so you can figure it will take a lot longer to bleach out the algae at the colder temperature.

    - - - Updated - - -

    Quote Originally Posted by TomAtlanta View Post
    Do you know if it effects the power of liquid bleach if it is kept in an unheated garage where it freezes and thaws, freezes and thaws, throughout the winter?
    This post describes the freezing point depression for bleach and for acid. The freezing point depression for 6% Sodium Hypochlorite as found in the older Clorox Regular and most Ultra brands of bleach is 7.3C or 13.1F so the freezing point is -7.3C or 19F. The freezing point depression for 8.25% Sodium Hypochlorite as found in the new Clorox and other brand of bleach is 9.7C or 17.4F so the freezing point is -9.7C or 14.6F.

    I do not think the bleach loses its strength due to freezing, but of course you have to be careful about having the bottle burst from expansion or develop cracks and then leak when thawed.
    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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