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Thread: First thread! How/why do I have calcium deposits forming on my gunite pool?

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    Join Date
    Jun 2016
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    Western Connecticut
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    First thread! How/why do I have calcium deposits forming on my gunite pool?

    Hi. First post! I had a pool installed last year and the pool company took care of it. This year (second year with pool), I started to care for it after the pool company opened it. Very early in the season, the pH went up above 8, and I lowered it with muriatic acid. However, I noticed that now the once-smooth walls have a sandpaper like feel to them. Not the entire wall and floor, but definitely in spots. It's not that bad, but definitely not the glassy smooth plaster from last year. Is there anything that I can do to help this or prevent it from getting worse? Was it just because of the pH? How quickly does calcium start to deposit when the pH gets too high? Thanks
    32,500 gallon in ground Gunite/White Plaster, Pentair Cartridge Filter, Pentair Propane Heater, Pentair Racer robot cleaner

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    Richard320's Avatar
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    San Dimas, CA (LA County)
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    Re: First thread! How/why do I have calcium deposits forming on my gunite pool?

    A combination of high pH, high TA, highish CH and low temperatures all contribute to scale formation.

    Hopefully you have one of the recommended test kits. Pool store testing won't suffice.

    If you take your (own) test results and plug them all into poolmath, down at the bottom you will see CSI. That's a calculated value. Zero is ideal. +/- .30 is just fine. As it goes above .3, the likelihood of scale formation goes up. Above .6 it's almost certain. Below -.3 and you start getting risky and below -.6 you'll start etching the plaster and weakening the grout holding your tiles in.

    So look at your CSI now. Then start playing with the numbers on poolmath. See what happens when pH goes way up. Then TA. Then CH. Temperature and CYA even affect it.

    Now you probably understand why.

    You want to be rid of it. If CH is way above recommended, and you have the option of replacing some water with lower CH fill water, do it. And then you drive down TA and maintain pH at the low end of swimmable (7.2>7.5) to get CSI done below -.3. And then you brush the scale with a stainless steel brush. Or get in and sand on it with some 320 grit wet-n-dry sandpaper. It won't lift immediately, but it should start shrinking some and be much smoother feeling. As you dissolve the scale, you will see the CH climb some. It has to go somewhere. It's a slow process. Think glacial speed. The alternative is an acid wash, and most likely the pool pros in your area are all too busy right now and you'd end up draining the pool right when you want to use it.

    There's a bit more here: Pool School - Calcium Scaling
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Join Date
    Jun 2016
    Location
    Western Connecticut
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    Re: First thread! How/why do I have calcium deposits forming on my gunite pool?

    Thanks!! I input all of the figures and it is coming out to CSI of .17, so I think I am OK. The scaling happened a few weeks ago when I didn't know what i was doing and the pH went really high. Now that I have all of the measurements under control, I hope that the problem won't get worse!
    32,500 gallon in ground Gunite/White Plaster, Pentair Cartridge Filter, Pentair Propane Heater, Pentair Racer robot cleaner

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