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Thread: Calcium Hardness...should I add?

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    Join Date
    May 2007
    New Jersey

    Calcium Hardness...should I add?


    I have gained great knowledge from the site in my first year as a pool owner. The info has been priceless. I have a fiberglass pool and had not added Calcium Hardness to my pool as of yet. I decided to purchase some at Leslies the other day and am ready to put into the water. The reason was that the debate seems unclear on whether to add or not to a fiberglass pool. Not sure what to do. I am leaning on putting it in as a just in case measure. Guidance?

    If I do put it in how is the best way to add to the pool water? Pantyhose like CYA? Skimmer? Over return? How long does it take to dissolve and show in tests? Is it safe to swim right after the addition of the CH?


    14 x 32 Fiberglass Pool 10K gal. Hayward Pump and Sand Filter. Autopilot SWG Dig 48 and Heat Siphon 3.25sx Heat Pump.

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  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD
    One manufacturer who sounded reasonably competent technically says that there should be calcium in a fiberglass pool to prevent cobalt from being leached out of the gelcoat. But I don't believe there has been any independent confirmation. For now I have been recommending 100 to 150 ppm of calcium for fiberglass pools. Others have other opinions, some quite different.

    Calcium chloride and calcium chloride dihydrate are both added to the pool by distributing the granules across the pool surface. It reacts vigoursly with water so you don't want to predisolve it or add it to the pool in a constrained area like the skimmer. You don't want to do anything that will raise the PH within 24 hours of adding calcium, no PH up, no shocking the pool, no baking soda.

    I wouldn't swim for 30 minutes after an addition and I wouldn't retest for four hours (both with the pump running).
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  3. Back To Top    #3
    mbar's Avatar
    Join Date
    Apr 2007
    Ashland PA
    I agree with Jasonlion - I have tried running the pool without much calcium (below 50), and had some stains - I also ran the pool with the calcium level at 300 and had stains. So now I run the pool in the 150 to 200 range. I have had very little staining this year, but I have also tried some other things too. One of them being using Proteams Metal Magic. After getting rid of the stains at the beginning of the season (used ascorbic acid and metal magic), I have not had any staining even with taking the water up to shock. I have added the metal magic whenever a lot of new water has been introduced to the pool. While it does cloud the water for a while, I don't seem to get any staining. It is too soon to say whether it is the metal magic or not, or the calcium level, or really pinpoint it completely, but this is the first year I have not had the stains occasionally appear . I will do the same thing next year and see how it works If we all keep track of what we do, and post our results, we should be able to keep the stains away. I hate stains!
    16x33 fiberglass pool sand filter

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