Calcium Hardness (CH) for Vinyl Pool Liners

[chem geek]

Ben,

Thanks for those links. This one says under "Calcium Hardness Check", "Calcium levels should be kept at a minimum level of 200 ppm to avoid corrosive conditions. Calcium levels over 500 ppm may cause problems such as cloudy water or scaling on the liner surface." (this link also says CH should be a minimum of 200 ppm). Of course, the "corrosive conditions" they are talking about are the ones people refer to for metal corrosion if there isn't a thin coating of calcium carbonate and that's a debatable and controversial topic (see this link for one such discussion) and they say nothing about low calcium doing anything specifically to the liner itself. Other CGT links refer to low pH being the real culprit along with very high chlorine level such as found by placing a Trichlor puck on vinyl (which is also low pH). They recommend using Cyanuric Acid, which as we know will reduce active chlorine level so reduce the effects of bleaching for the medium blue that is apparently the only one affected by chlorine.

The link from giroup01 (thanks for that) says the CH should be a minimum of 100 ppm. However, the lab studies looking at different water parameters found that low and high pH were the most problematic while high chlorine levels could fade vinyl and also accelerate the effects of low pH. The ideal pH was between 7.0 and 7.5. Below 7.0 there was in increase in wrinkling, loss of tensile strength, elongation and fading. Above 7.6, the vinyl loses weight and expands. As for chlorine, it should be noted that they had a starting CYA level of 100 ppm which is rather high. The FC of 20 ppm in these conditions adversely affected the vinyl (interestingly, this is only an active chlorine level of somewhere between 0.1 and 0.4 with equivalent FC with no CYA of 0.2 to 0.8 so not really that high and we've had people shock with an FC that is up to 40% of the CYA level without bleaching liners, so I don't know why they saw that unless the chlorine test didn't have CYA the way their pH test did). Unfortunately, they did not test for varying CH, but since their tests were at a CH of 100, that at least doesn't seem to be a problem level in the short-run.

Richard

[CarlD]

It's beginning to look like empirical evidence from users may be the proper foundation of a test protocol. But there has to be a quantifiable way to measure damage to the liner, compared in a double-blind setup.
In other words, you first have to model a behavior/reaction and then control conditions and have a viable measurement methodology.

Guess I've been in clinical trials programming too long!

Carl

[PoolDoc]

@ Carl, the real problem with ever testing liners is that it is apparently impossible to take that info to the consumer.

The product engineer I spoke to yesterday told me that there are substantial differences in the durability of one liner compared to another, but that he knew of no way a consumer could tell which was which. He even told me that sometimes liner makers use sheet from one mfg for the liner body, and from another mfg for the 'tile line'.

So, unless you had an exhaustive set of liners, and tested all of them, you couldn't determine which rules applied to all liners, and which were specific to a subset of them. Worse, even if you did determine that data, consumers couldn't use it, because they usually would not able able to determine which grade and source of vinyl sheet was used in THEIR liner.

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@ Chem_Geek,

you can read them for yourself (and probably have) but the water guides looked like boilerplate pulled from chem mfg releases, rather than anything from internal liner testing. One page even referenced a Biolab source.

Regarding pH, the engineer was pretty insistent that anything between 5 and 9 was fine.


Ben

[chem geek]

I agree with you about the water guides being a boilerplate so not very helpful in figuring out whether saturation with calcium carbonate is really needed.

I got some more info I posted here at TFP where the most interesting information is that 1) calcium carbonate levels below 7% in vinyl do not significantly affect its physical properties and 2) that at such low levels even acidic conditions didn't result in a loss of flexibility and relatively little loss of weight.

So to me this means that low levels of calcium carbonate in vinyl pool liners probably wouldn't require saturation of calcium carbonate in the pool water. Though high levels of calcium carbonate in vinyl might require such saturation, such high levels are stiffer vinyl that is more susceptible to acidic conditions and general chemical attack. So hopefully, most vinyl pool liners don't contain such high levels of "filler" calcium carbonate. It's too bad there isn't an easy way to tell, though if one had a sample of the vinyl then I suppose one could see the weight loss when exposed to very acidic conditions since that presumably roughly measures the calcium carbonate content. Unfortunately, most people won't have a piece of spare vinyl from their pools let alone accurate scales and even then this test may not be definitive.

[CarlD]

Oh, I understand that there are many difficulties in setting up a test protocol. Even if we could give 100 people liners made by two different methods and test them over 5 years you would have trouble isolating out meaningful results due to variations in water condition, air temp, exposure to sunlight, levels of chlorine, pH, etc, that don't allow you to control for high and low calcium water. For the moment all we have is the testimonials of owners who have had vinyl pools for years with low calcium levels. This is, at best, very poor data, because we don't know what our population is, and we can guess that our sample is probably skewed. That's my side of the fence, the clinical trial issue.

Your side of the fence is establishing a mechanism where low CH can be shown to degrade various vinyls while high CH doesn't degrade the matched vinyl samples. You know, the chemistry side that I don't understand.

In the meantime, our anecdotal information tells us that CH for vinyl is...not proven to protect it.

Carl

[Spensar]

I bought my house 8 years ago with the pool. The liner was vinyl and 20 years old. The old owner hadn't done much to look after the pool and neighbours said they kept it from being green by tossing chlorine in it. What finally did the liner is was that it is a rectangular pool with square corners and the vinyl gave out at the corners. I have a very good pool tech that only does service, and doesn't sell chemicals and products, etc. and he inspected it when I bought the house. At that time he gave the corners 2-3 more years, and he was on the money.

Don't know if this adds anything to the discussion among the knowledgable here, just sharing experience with an very old liner.

[chem geek]

Thanks Spensar. Where you using bleach or chlorinating liquid the entire 8 years since you had the pool?

[Spensar]

Thanks Spensar. Where you using bleach or chlorinating liquid the entire 8 years since you had the pool?

Sorry, missed the question, so very late reply. 90% liquid chlorine, mainly calcium chloride and mainly at the beginning before finding this forum.

[AnnaK]

Late to this thread. If you're still interested in data points, here's mine:
+ 7 year old vinyl liner
+ have never added calcium
+ fill water has 52 mg CaCO3/L
+ pH 7.5
+ CYA 50 ppm
+ use 12% LC and trichlor

No damage, no wrinkles, nothing adverse to report regarding the liner. Some fading from sunlight - the area covered by the steps is darker than the rest of the pool.