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Thread: Plaster dust after bringing CH down

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    gtemkin's Avatar
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    Jun 2008
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    Seattle, WA
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    Plaster dust after bringing CH down

    For a couple of years I had been living with a CH in the 475 to 525 range. Wasn't too much of a problem to work with; my CSI hovered around zero give or take a couple of tenths.

    This last winter we had a lot of rain and I've been able to use rain water so I'm now at the 275 point and my CSI is generally more negative than it has been in the past.

    I noticed when brushing the pool I'm getting white clouds that look just like the plaster dust I had when the plaster was fresh.
    Here's my numbers (TF100):

    PH 7.4 (coming back up from a TA adjustment of 90 down to 70) In the past usually settled at 7.8
    FC 5
    CC 0
    TA 70
    CH 275
    Borax 0
    CYA 40
    Temp 62F

    Water is crystal clear (except after brushing), no evidence of any algae.

    Is it possible that the former period of elevated CH deposited a micro layer of invisible scale that is now loosened by the the lower CH and CSI numbers? I did purchase a stainless steel bush but I noticed the same situation when I was still using my plastic brush. Also have the appearance of 3 small spots of what looks like underwater effervescence which showed up over the winter. Water has been too cold to get a feel for what they are.

    Thanks.
    21K gal 16' x 40' in-ground pool built 1959, old school with Jacuzzi bronze pump, American Products 24" Sand Filter & Americana Multiport valve, Jandy Lite2 millivolt heater, Coverstar cover, and classic Kreepy Krauly.

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    duraleigh's Avatar
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    Apr 2007
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    Sebring, Florida
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    Re: Plaster dust after bringing CH down

    Is it possible that the former period of elevated CH deposited a micro layer of invisible scale that is now loosened by the the lower CH and CSI numbers?
    Possibly. Only a guess but I could envision that the lower dissolved CH in the water is loosening a tiny bit of scale from your walls.

    I would think the CH would simply go back into solution but I cannot think of another cause.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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