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Thread: Copper heat exchangers and low calcium

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    Copper heat exchangers and low calcium

    My CH is 80 ppm (vinyl liner)

    Anyone have anymore scoop on low calcium potentially causing the liner to skrink up over time?

    Also, the industry line ive heard is that the copper heat exchangers in the pool heaters could be damaged by low calcium. True? Untrue? Any hard data to indicate one way or another?

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Copper heat exchangers and low calcium

    Low CH is fine in a vinyl pool, even with a heater with a copper heat exchange coil. There have been thousands of pool years of experience with low CH levels and the worst problem so far has been some rather rare foaming that could have been prevented by higher CH levels.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Copper heat exchangers and low calcium

    The ability of saturated calcium carbonate (i.e. a saturation index near zero) to protect metal from corrosion is controversial and not clear. You can read some of the controversy from experts here. Low pH is the worst factor for corrosion. After that, it's probably high oxidizer levels, so high FC with no CYA. High salt (chloride) levels also increase corrosion rates, especially to stainless steel (and probably aluminum). For gas heaters, one of the biggest factors is physical corrosion (including removal of any protective layers) from water flow so heat exchangers with tight bends tend to fail sooner than those with curved spiral geometry.

    Many municipal water supplies have low Calcium Hardness (CH). My own tap water has a CH of around 50 ppm and the Total Alkalinity (TA) is around 80 ppm. The pH is around 7.7. This all goes through copper pipes. The district does use some corrosion inhibitors, including 300-500 ppb phosphates.

    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Copper heat exchangers and low calcium

    The commonly used Langelier Santuration Index, the less commonly used Ryznar Index, and our own CSI that we use here are great at predicting the scaling propensities of water, not so great at predicting the aggesiveness of water against plaster surfaces, and totally useless to predict the corrosiveness of water on metal surfaces. However, since this is actually a very complex subject our industry, which doesn't always have the brightest bulbs working in the field, tend to incorrectly simplify things and then you get the confusion about calcium protecting heat exchangers from corrosion. It is actually the deposit of scale that will form because of the elevated temperature in the exchanger that can help prevent against corrosion but it's pH and the absence or presence of other ionic species in the water (such as sulfates or chlorides) that are much more important factors in how corrosive toward metal the water is.

    As far as vinyl liners, CH doesn't matter at all (except at the high end where it can lead to scaling conditions) but low pH will damage a liner by leaching the plasticizers out of the vinyl and actually attacking the vinyl itself.

    There does seem to be evidence that CH is important in fiberglass pools to help prevent cobalt spotting and to reduce the propensity of fiberglass to stain.

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