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Thread: Water Hardness (Calcium) and Vinyl hot tub (Softub)

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    Water Hardness (Calcium) and Vinyl hot tub (Softub)

    I have been getting conflicting information on this and was hoping someone here could clarify for me.

    I found out from our local pool shop that the water in my area (near Seattle, WA) is some of the softest and metal-free water in the country. They said I don't need to use things like "Metal Gon" or a pre-filter since there's basically nothing to filter anyway, but at 20ppm hardness I'll probably need some hardness increaser. They said I should strive to get at least 100ppm.

    My hot tub is a Softub with a soft vinyl inner lining. I called Softub and they said I should strive for 250-400ppm for water hardness (or at least, they said I should strive to make test strips read that number range). They also, of course, say I should use their "Softcare Calcium Up" product exclusively. That means pretty much a whole bottle of their product for every refill of my hot tub given how soft my water starts out at!

    While trying to search for info on potentially cheaper sources of calcium, and if they would be as safe to use, I found several threads here that said that vinyl-lined pools didn't need calcium at all! Is the vinyl in pools significantly different than the vinyl in Softubs, and that's why Softub says I need 250ppm or risk the vinyl hardening and cracking from the water leaching the calcium from the vinyl? Or is Softub just playing it safe and I don't really need to worry about water hardness and the calcium leaching thing is a myth?

    So essentially not sure who to believe and if I should aim for 250ppm, 100ppm, or just leave it alone at its default 20ppm.

    I was about to order this as a cheap source of calcium - https://www.amazon.com/Pool-Spa-1900.../dp/B00PZZFAAA But I don't know for sure what form of calcium it is, nor if that really matters? Is any kind of water hardness increaser equally fine to use on a vinyl-lined hot tub? My local shop wanted to sell me SpaGuard brand but it's $11 for 12oz (same as Softcare Calcium Up) compared to $12 for 5 pounds if I get this Clorox stuff from Amazon...

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    Mod Squad pooldv's Avatar
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    Welcome to TFP!

    We are in the midst of a discussion about appropriate CH levels in a hot tub and haven't reached a conclusion. Our guideline has always been 125 ppm of CH is good for the tub for two reasons. First, it will reduce or eliminate the potential for the water foaming if there is a problem with that and everyone agrees on that. Second, it helps extend the life of the heater. There is so easy discussion whether 125ppm is enough or if 200-250ppm would be better. So, you will receive unanimous consent that 125ppm is a good number for chin a hot tub. Pools are different because the heaters are different. And foaming isn't an issue.

    More here about cheap sources of chemicals, Pool School - Recommended Pool Chemicals
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    I assume you meant Calcium instead of Chlorine, but in any case Softubs don't actually have a heater, not in the traditional sense. They just pump the water through a spiral pipe that surrounds the pump motor itself, and the water is heated by the waste heat from the pump motor. So there is no direct contact between water and a heating element like there is in a traditional hot tub. Softub only mentions water hardness as an issue in relation to the vinyl lining and soft water leaching the calcium out of the lining.

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    Mod Squad pooldv's Avatar
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    Ahaa. Yes, I did mean CH, dang autospeller. Ok, with no heater then no reason to worry about CH level unless there is an issue with foaming.
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    So Softub claiming lack of CH will leach the calcium out of the vinyl and make the vinyl lining crack etc is nonsense?

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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    Yes. There is no calcium in vinyl to be leached out.


    How is Vinyl Made?
    Vinyl is essentially derived from two simple ingredients: petroleum and salt. Petroleum or natural gas is put through a process, called cracking, to make ethylene, which is combined with the natural element chlorine to produce ethylene dichloride. Another cracking process transforms ethylene dichloride into a gas called vinyl chloride monomer (VCM). Finally, through a process known as polymerization, the gaseous monomer is converted into a fine, white powder - vinyl resin. However, one more step remains before the resin becomes a usable material.

    Besides looking very much like flour, vinyl resin is analogous to flour. Both are of little use, by themselves. However, just as flour can be combined with other ingredients to make a moist cake, a flaky pie crust, or a variety of breads, vinyl resin can achieve various desired properties suited for a variety of end-products once it is combined with selected chemical additives and modifiers. The diagram below illustrates this process

    More here, About Vinyl & PVC
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    One has to wonder why they make such a claim in the first place, or where they got that idea from...

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    Mod Squad pooldv's Avatar
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    Yes indeed. I have never heard any such thing in all my born days.

    Maybe they got confused about plaster? If there isn't enough CH in the water in a plaster pool calcium will be leached from the plaster.
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    Vinyl end products have proprietary compositions based on the engineering performance needs and the desired aesthetic qualities as well as the manufacturability. Most vinyl products incorporate some amount of calcium carbonate into the polymer melt to improve the mechanical properties of the final product as well as aid in the manufacturing process. Calcium carbonate (purest form) is a white to slightly off white color and so it allows the vinyl to achieve a white enough base color to make pattern printing possible (titanium dioxide is a brighter and cleaner white color but it also much more expensive to add).

    So the question is - does an undersaturated (corrosive) water environment leach out any measurable amount of calcium and, if so, does that do any structural or physical damage to the vinyl?

    The answer is - no one knows for sure. It all depends on how much calcium carbonate is present in the material, how the material is manufactured and how easily calcium can leach from the vinyl to the water. Because of the great degree of variability in vinyl products, there is no one specific answer. To the extent that manufacturers want to protect themselves from product liability and defectiveness claims, they will always quote APSP swimming pool standards and claim that you need 200-400ppm CH to protect the vinyl. There is no scientific justification for this claim, it is a legal claim.

    The overwhelming evidence from thousands of TFP users with vinyl pools is this - CH seems to have no correlation to vinyl liner lifetimes. A specific CH value or range does not confer any protective effect onto vinyl liners nor does it correlate with any specific lifetime traits. Vinyl pool owners typically keep a certain level of CH in their pools to avoid foaming but, other than that, do not routinely try to adjust their CH levels. Calcium can scale onto a vinyl surface and cause surface roughness, but that is only found to happen when the pH, CH and TA are also well above normal ranges and the scaling would occur regardless of pool surface type.

    So, for your spa, you very likely only need about 150ppm CH to stave off foaming and not much more than that. Unless the manufacturer has some specific data or evidence they are willing to share (and they likely do not) then it's impossible to evaluate their claims. If you value the warranty that they have offered you (I, for one, don't consider most warranties worth the paper their printed on), then follow their recommendations.
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    There are 3 major ingredients in the chemical makeup of a vinyl liner:
    PVC (Poly Vinyl Chloride) is the main building block that goes into creating vinyl liners. PVC makes up 50%-60% of the total raw ingredients.
    Plasticizer (petroleum-based oil) is another key ingredient that makes up 35%-40% of the total raw ingredients. This ingredient determines the flexibility of the liner and increases its chemical resistance and life span.
    Inert Materials (calcium carbonate a.k.a. clay) and Stabilizers make up 11%-30% of the total raw material ingredients.
    The Truth About Doughboy Liners | Zagers Pool and SpaZagers Pool and Spa
    Did you know that Vinyl liners contain calcium?
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    Yeah that was the thread I saw before, but I wondered if hot tubs (or Softubs in particular) were somehow different than pools (different kind of vinyl?).

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    Mod Squad pooldv's Avatar
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    Re: Water Hardness (Calcium) and Vinyl hot tub (Softub)

    Well, how about that? All these years and so many thousands of threads read and I missed that one. I still learn stuff on TFP!

    Seems to me that 125ppm of CH is still a good idea.
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