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Thread: Plaster pitting

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    Plaster pitting

    I'm having some pitting problems with my plaster, and the pits are gathering alge.
    Trying to figure out why it's pitting like this. Getting worse.

    The pool was replastered 5 years ago.

    My PH always runs high and I use acid every few days to bring it down.

    CH is 200
    TA is 80
    PH is 7.6 today
    Cya 35
    FH 3
    Water temp 77f

    Been using bleach in pool for 5 years and water always looks good but I do get these algae spots in the pits.

    Any ideas?

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    Mod Squad pooldv's Avatar
    Join Date
    Aug 2012
    DFW, TX

    Re: Plaster pitting

    The pitting is called etching and results from having low CH causing calcium to dissolve from the plaster into the water. To prevent etching you need to manage your CSI between -0.3 and +0.3. This is done by entering all of your test results in Poolmath and it will calculate your CSI. Adjust CH, TA and PH to get the CSI into range. Your CH needs to be a minimum of 250, 350 if you have saltwater.

    More here, Pool School - Recommended Levels
    And here, Langelier and Calcite Saturation Indices (LSI and CSI)

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