Calcium Hardness (CH) for Vinyl Pool Liners

[PoolDoc]

Hi Richard, All;

Richard, if you can dig to the bottom of this, it would be very helpful to many. I did some work on it years ago, but ran into problems and gave it up. A lot of my info came from a product engineer at Canadian General (http://www.cgtower.com/). At that time (15 years ago), they were making a big part of the PVC sheeting used by US liner mfgs.

What I learned from him was the following:
+ calcium carbonate is used as filler in some, but not all (he thought) sheet.
+ low calcium was not (he thought, supported by some casual testing) going to cause premature failure.
+ like other flexible PVCs, vinyl sheet is a mixture of PVC, plasticizers, UV stabilizers, colorant, filler, and ??
+ there is no standard formulation.
+ liner color may, or may not, be in the sheet.
+ liner patterns are printed on by the liner mfg.
+ at that time (as I recall) he thought that NONE of the liner mfgs were sheet mfgs.
+ there were 2 or 3 mfgs of sheet.
+ sheet formulation was proprietary and varied from company to company, but also from time to time.
+ the same model & weight of liner might be actually made from 3 or 4 different instances of sheeting, each with different composition and properties.
+ many of the liner mfg did not understand the intricacies of PVC mfg, and thus did not understand what they were buying. There particular concerns often focused on manufacturing properties, like print-ability and suitability for their equipment.
+ printing ink varies too, and there's no guarantee that the ink for a particular model is the same over time.
+ generally, low pH tended cause plasticizer leach-out, but he didn't have data tying time and pH to damage.

Bottom line for me: there was no way to tell from one liner to another, or even from one liner today to the same liner tomorrow, and thus there was no valid way to get very specific about what would affect which liner in what way. Even with the minimal exposure to liner pools I've had, I've seen big differences in liner life expectancy in similarly managed pools.

Ben

[PoolDoc]

Whoop! Whoop! Whoop!

CGT is now making finished sheeting and has a BUNCH of tech data:
http://www.cgtpoolliners.com/cgt-technical-manual.htm

I'll archive copies, but don't have time to read it all now.

Ben

The content in this one will be particularly of interest:
http://www.cgtpoolliners.com/cgt-tec...bulletin-4.htm

(I lied; I've ended up reading quite a bit as I archived. A lot of the data dates to 2007)

[PoolDoc]

Ok, I got side-tracked, and called CGT. I'm ADD and eternally curious; whaddya expect?

Spoke to a liner product engineer, "Immanual + foreign last name" -- it bugged him that I couldn't understand his name, I so I gave up. After we spoke for awhile, he transferred me to "Carl Flieler" (sp?) => Carl Flee-ler who is the pool liner guy, but he wasn't in.

Anyhow:

+ OK pH range is 5 - 9
+ The idea of adding calcium carbonate scared him, because he said high pH is more damaging than low pH.
+ There are definitely variations in liner material quality, and there is imported knock-off material. But he thought the patterns (see website) are likely to indicate source fairly well.

Richard, you might want to talk to 'Flee-ler'.

Ben

[giroup01]

http://piscines-apollo.com/docs/chemicals_and_vinyl.pdf

[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.

=====================================

@ 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.