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Thread: New Pool Plaster does not always cause CH rise

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    New Pool Plaster does not always cause CH rise

    In some circles of the pool industry, it is believed that calcium “naturally” releases from a new swimming plaster surface while it cures, (or more accurately, hydrates), and thereby continuing to increase the calcium hardness (CH) of the pool water during the first several months. This is a false belief.

    However, if the tap water used to fill the freshly plastered pool is aggressive, then yes, calcium will be dissolved from the plaster surface, thereby increasing the CH level of the pool water during that process. The pH also rises in this situation. In fact, even balanced (zero CSI) tap water will usually dissolve a small amount of calcium when it first comes into contact with a new plaster surface.
    Furthermore, when the TA of the tap water is low, the higher the pH will become after filling. The best way to combat the pH rising above 8.5 as the pool fills, is to raise the alkalinity content of the fill water before it even goes into the pool. Adding sodium bicarbonate to the tap water (to raise the TA above 200 ppm) before it is used to fill the pool is the best way to prevent the pH from soaring so high. This also helps prevent calcium from being dissolved from the plaster surface.

    During the first month, a plaster surface becomes sufficiently hydrated and carbonated, which means it becomes less soluble. After one month, if the water is in balance (zero CSI), it is unlikely that any additional calcium will be dissolved from the plaster surface. If the plaster quality is good, there is no “natural” tendency for calcium to be released from pool plaster. Calcium levels do not automatically rise, and therefore, low levels of CH should be corrected immediately.

    A good general recommendation for new plaster pools is to raise the calcium level to a minimum of 200 ppm, the TA to a minimum of 120, and to ensure that the CSI is a slightly positive number as soon as possible and during the first month. The main point being, new pool plaster requires a positive CSI (for one month) to protect it and to prevent a loss of calcium from the surface. If that is followed, then very little calcium will be dissolved from the surface, ensuring a smooth, dense, durable, and long-lasting plaster surface.

    However, this is contingent on the plaster quality being good. If there is any continued and significant increase in the calcium level after one month has past (accounting for evaporation or Cal Hypo additions, etc.), it is possible that the workmanship of the plaster was sub-standard.

    See this post: aggressive-water-versus-improper-pool-plastering-t51900.html

    See also this post: ten-guidelines-for-quality-pool-plaster-t42957.html

  2. Back To Top    #2

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    Re: New Pool Plaster does not always cause CH rise

    Really interesting post...We just had to have our pool repaired and completely re-plastered. I haven't had any issues with CH, I do, however, seem to be fighting with the TA and high pH.
    28,000 Gal Pool w/ Attached raised Spa, White Plaster Finish, D.E. Filter - FNSP 60 sq. ft., Whisperflo Pump, Nature 2 Element (Housing Only Now Devoid of Cart.), Hayward CL200 In-Line Automatic Pool Chemical Feeder, RayPak Gas-fired Heater, Polaris 380, Zodiac 1.5-HP 240-Volt Polaris QT Spa Blower

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    Re: New Pool Plaster does not always cause CH rise

    Plaster pools do cause the pH of the water to rise significantly for the first month, but after one month, it has a very small effect. After one month has past, the main reason for pH rise is due to high TA. Assuming that your re-plaster job is more than one month old, I suggest bringing down the TA now if higher than 100 ppm to about 80 ppm, and that will help slow down (but not stop) the continuous pH rise. But be sure that the CH of the water is high enough to offset the lower TA. This forum's CSI Calculator can help you with that aspect of water balance. The type of chlorine being added also needs to be considered for best TA parameter to maintain.

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    Re: New Pool Plaster does not always cause CH rise

    Thanks for the info...will report on my progress!
    28,000 Gal Pool w/ Attached raised Spa, White Plaster Finish, D.E. Filter - FNSP 60 sq. ft., Whisperflo Pump, Nature 2 Element (Housing Only Now Devoid of Cart.), Hayward CL200 In-Line Automatic Pool Chemical Feeder, RayPak Gas-fired Heater, Polaris 380, Zodiac 1.5-HP 240-Volt Polaris QT Spa Blower

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    Re: New Pool Plaster does not always cause CH rise

    Performed water test today and TA is back up to 180 and pH is at 8.4. Added 1 Gal Muratic Acid (31.25%). Will retest in the morning.
    28,000 Gal Pool w/ Attached raised Spa, White Plaster Finish, D.E. Filter - FNSP 60 sq. ft., Whisperflo Pump, Nature 2 Element (Housing Only Now Devoid of Cart.), Hayward CL200 In-Line Automatic Pool Chemical Feeder, RayPak Gas-fired Heater, Polaris 380, Zodiac 1.5-HP 240-Volt Polaris QT Spa Blower

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