AG vinyl liners & calcium hardness

[SunnyOptimism]

I would like to make a technical point that is often "incorrect" in my opinion - vinyl liner pools do need a certain level of calcium in the water for two very different reasons.

#1 - calcium acts as an anti-foaming agent in water. A concentration of 120-200ppm is all that is needed to arrest foam formation.

#2 - unfortunately there's not a lot of good technical literature on this subject but many polymers, vinyl included, use cheap calcium carbonate additions (along with plasticizers, release agents, etc) as "additives" to the polymer matrix. Calcium carbonate modifies the tear strength and hardness of vinyl. So, in a residential pool, water with no calcium and low pH can strip calcium from the vinyl liner material if calcium carbonate is used as a filler material. Unfortunately, there's no way to know how much calcium is used but I have heard figures quoted as high as 7-10% by weight. Only the actual liner manufacturer would know the details of the vinyl starting materials that they use.

Just a minor point to make. Calcium is going to get into your pool water one way or another, so unless you go out of your way to reduce it and keep your pH unnaturally low, CH (calcium hardness) is not a big deal for vinyl pools.

[PoolDoc]

1. Re: "anti-foaming" properties of calcium -
=> I can't recall having seen ANY reports of pool foaming what weren't preceded by quaternary ammonia algaecide use, so you seem to be proposing to use calcium to solve a problem that doesn't -- as far as I can tell -- even exist. (Independent spas are a special case, and we don't get into detached spa chemistry here.)
=> Even then, I'm not aware of any anti-foaming properties of calcium hardness EXCEPT with respect to soap. But if there is soap in a pool, they've got bigger problems than low calcium.

2. Re: calcium in vinyl -
=> You are entirely correct to say that there seems to be little scientific literature on the composition and durability of vinyl sheeting. I've been looking for years, and have never found ANY.
=> Consequently, dogmatic assertions in literature promulgated by pool chemical manufacturers -- INCLUDING the older versions of the CPO training manuals -- certainly originates in their self-serving desire to sell chemicals. The absence of scientific studies doesn't prove that calcium is unneeded, but it certainly proves that they don't KNOW whether it's needed or not.
=> I have had several off-the-record conversations with product engineers at North American manufacturers of vinyl sheeting. None of them could absolutely rule out the possibility that increased calcium levels would preserve some 'flavors' of vinyl sheet, but all of them doubted that that was the case; none of them had seen evidence to support that idea. Please note that, as far as I know, NONE of the vinyl liner makers actually manufacture the vinyl sheet used in their products.
=> In the nearly 20 years since I first published the page on PoolSolutions questioning the value of calcium in vinyl pools, I cannot recall ANY evidence that soft water caused premature liner failure.
=> None of this proves for a certainty, that calcium has no particular value in vinyl pools, but certainly renders any claim that calcium DOES have value highly suspect.

So . . . if you have DATA to support your claims, I'll be happy to open up the "China Shop" section to you, and allow you to argue your case. If you can prove your claims, I'll revise our position to reflect what you're able to prove.

But otherwise, I'll pretty much insist that you keep this opinion to yourself.

[chem geek]

The use of calcium to reduce foaming makes sense in spas (waterbear has recommended 120-150 ppm and that seems to work well in spas) where foaming can be more common due to the low water volumes so high bather load, but in a pool it's not normally a problem as Ben noted.

As for calcium and vinyl liners, this was discussed in a thread at TFP where I wrote this post that notes that acid, not low calcium, can be a problem but mostly when higher calcium carbonate fill levels are used in the liner. Though it may be possible that vinyl liners with high calcium carbonate might need some CH in the water, that's not a certainty and as noted in the references such high calcium carbonate content has other negative properties.

So the original post by SunnyOptimism isn't just an opinion, but based on some information from other sources though extended and possibly misinterpreted. One should always reference original sources whenever possible, not only for proper attribution to them but also so people can find more details, determine proper context, and draw their own conclusions.

[CarlD]

The use of calcium to reduce foaming makes sense in spas (waterbear has recommended 120-150 ppm and that seems to work well in spas) where foaming can be more common due to the low water volumes so high bather load, but in a pool it's not normally a problem as Ben noted.

I'm guessing that this is actually creating what is called in household water, hard water, which is why water softeners are popular (we have one). Hard water is notorious for being difficult to form suds in, for breaking it down quickly, and, of course, for leaving scale on everything. So it makes sense that if you make the water harder, foaming/sudsing will be more difficult. I realize this is different in that hard water is usually other metals, particularly iron and copper, but calcium is, of course, a highly reactive metal, but a metal nonetheless.

[SunnyOptimism]

So the original post by SunnyOptimism isn't just an opinion, but based on some information from other sources though extended and possibly misinterpreted. One should always reference original sources whenever possible, not only for proper attribution to them but also so people can find more details, determine proper context, and draw their own conclusions.

I saw this post pop up again on the "What's New" page and I was curious...actually I wish this post had just been deleted but Ben decided to keep it.

As for some background, this thread was not actually an "original post" by me but a quick response (I'm going to stop doing the "quick response" thing) to another OP who was asking about calcium and vinyl. The funny thing is, my response to the OP got me in "hot water" with Ben because it was one of my first posts and it made me sound like I was someone who was in the pool biz trying to lead pool owners astray. It was quite funny actually but Ben and I sorted it out through e-mail and he decided to split this comment off and put it in The China Shop.

WARNING - SPECULATION TO FOLLOW (Ignore if you don't like speculation)

I'm still not convinced or think there is any good solid scientific evidence of what calcium does for vinyl liners. There's certainly lots of anecdotal evidence and it does point to the answer being "it's not really that important". That being said, I have a Master's Degree in Materials Science and Engineering and I've studied both polymer materials as well as inorganic semiconductor materials extensively and my technical "gut feeling" says there's something there but perhaps it's just a small effect and not all that relevant to pools.

Calcium carbonate is primarily a fill material in PVC and it has been used since the large scale industrial manufacturing of PVC began. It has multi-faceted uses by both modifying the polymer macro-structure and thus changing the mechanical properties of the final product to also allowing coloration of the PVC as calcium carbonate is a decent "white" colorant. However, all that I have read and can find journal articles on (my access to scientific journals these days is quite limited), is that calcium carbonate is used primarily as an extender - it's mixed in with the PVC so that the manufacturer uses LESS PVC starting material (expensive) and MORE inert volumer filler (cheap). Think of it like sausage making - you can sell more sausage if the starting meat you use is fattier.

Calcium carbonate also changes the extrusion & forming properties of the material as it is manufactured into various shapes (pipes, sheets, etc). The amount used in terms of volume fraction is typically controlled at the factory and is based solely on "what works for the forming equipment" and not for any good scientific reason. This, I believe, is why two different vinyl liner materials can have different levels of calcium carbonate in them, it's all factory dependent.

I can see low pH as a definite problem especially if the carbonate packing fraction is high enough to allow the particles to form a connected matrix. Low pH would tend to convert the less soluble carbonate into more soluble calcium chloride and thus deplete any carbonate material in the near surface region of the PVC that is in contact with water. I bet if you looked at a sample of old PVC liner material that was exposed to low pH under an electron microscope in cross-section, you'd probably see a surface region of the PVC with depleted calcium and a bulk region with normal calcium levels.

Two other uses of calcium carbonate in PVC that I found interesting were these -

1. The PVC synthesis process creates excess HCl as a byproduct of the organic synthesis reaction. Calcium carbonate is good at scavenging excess HCl from the material after it is synthesized and used during the manufacturing of PVC parts. Again, this is motly to protect the manufacturing equipment from corrosion by acid exposure, not necessarily to protect the end user

2. Fire-retardant - calcium carbonate releases CO2 gas during burning and that CO2 can be used to help suppress a fire. Also, when PVC burns, it can release HCl gas which the carbonate would tend to neutralize.

So, in summary, what does this mean for pool liners.......no idea! But this is The China Shop and I was told we are allowed to speculate here, so you all can draw your own conclusions.

[chem geek]

I'm guessing that this is actually creating what is called in household water, hard water, which is why water softeners are popular (we have one). Hard water is notorious for being difficult to form suds in, for breaking it down quickly, and, of course, for leaving scale on everything. So it makes sense that if you make the water harder, foaming/sudsing will be more difficult. I realize this is different in that hard water is usually other metals, particularly iron and copper, but calcium is, of course, a highly reactive metal, but a metal nonetheless.

Hard water is usually from magnesium and calcium, not from iron or other metals that aren't very high in concentration. Magnesium and calcium form a precipitate with soap such as magnesium or calcium stearate. This is why soap doesn't suds well in hard water and how soap scum forms. To reduce foaming in spas, one could use magnesium instead of calcium if one wanted to.

[chem geek]

I can see low pH as a definite problem especially if the carbonate packing fraction is high enough to allow the particles to form a connected matrix. Low pH would tend to convert the less soluble carbonate into more soluble calcium chloride and thus deplete any carbonate material in the near surface region of the PVC that is in contact with water. I bet if you looked at a sample of old PVC liner material that was exposed to low pH under an electron microscope in cross-section, you'd probably see a surface region of the PVC with depleted calcium and a bulk region with normal calcium levels.
:
So, in summary, what does this mean for pool liners.......no idea! But this is The China Shop and I was told we are allowed to speculate here, so you all can draw your own conclusions.

Because we haven't had ANY reports of vinyl problems with little or no calcium in the water over more than a decade, the theoretical issue of calcium carbonate depletion from vinyl may be possible but in practice not an issue. Whether this is because the percentage of calcium carbonate filler content is below the 7% that the sources I had referenced indicated is the amount above which the characteristics of the vinyl become problematic, including susceptibility to acid, I don't know. This is consistent with what you are speculating, but again since we don't see problems in practice there is no need to worry people about it even by mentioning it as a theoretical problem outside The China Shop.

[CarlD]

Hard water is usually from magnesium and calcium, not from iron or other metals that aren't very high in concentration. Magnesium and calcium form a precipitate with soap such as magnesium or calcium stearate. This is why soap doesn't suds well in hard water and how soap scum forms. To reduce foaming in spas, one could use magnesium instead of calcium if one wanted to.

OK....so I was right for the wrong reasons! It IS creating hard water in spas just to reduce foaming.