Need some basic advice -TA, pH, CH, FC all things chemical

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PowerPigg!! said:
The referred study appears to be dated 2019. Things seem to have changed since according to this 2021 post.

Link to 2021 comments on similar question
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I had trouble with the link. Do you mean this thread?

Calcium Hardness , Vinyl Pool Liners and Pool Math

Hi, this is my first post. I am opening my pool with the help of the TFP Pool Math mobile app and also by reading TFP forums - but I have some questions. I have recently read many posts from TFP experts that if you have a vinyl liner it doesn't matter what your calcium hardness is. If I have...
www.troublefreepool.com www.troublefreepool.com
It continues to state no calcium in vinyl; no need to worry about CH in vinyl pool (a reasoning that goes back at least a couple decades and as you point out, recently repeated). Hence the thinking behind my post; should this be reexamined (It would seem so).
 
@SoDel

This topic has been discussed many, many, many times on TFP both in open forum and behind the scenes (yes, we guide/mod/expert folks talk amongst ourselves). The short answer is this - most vinyl liner manufacturers get their starting vinyl materials from different source manufacturers. Those vinyl sources all use proprietary recipes for their finished products and none will disclose what specific compositions they use. Therefore, short of some exhaustive, reverse engineering study of dozens of different liner materials, there is no way to know exactly how much CaCO3 is used or how susceptible it would be to leaching. There is also a further complication given the fact that liner makers will often use different material batches in the same liner fabrication. So there is really no way to know what a particular liner will do.

That said, the recommended levels for vinyl are set in such a way to create comfortable water that is free of foaming . For a vinyl pool, controlling saturation balance is more important for the equipment pad (not scaling calcium in an SWG, etc) than it is for the pool surface.
 
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I'm glad I've started reading this forum more regularly. "Secret vinyl liner recipes" is not information that would have come up in my usual internet surfing.

I can't wait to tell my kid that an aspiring pool liner must survive a 2-week battle against a "pink staining organism" with no ill effects before it is worthy of the name. My mind's eye keeps picturing Pinky from the Doom video games as the "organism" in question.
 
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SoDel said:
1. Maintain CYA at 30 to 50 ppm (at least to this point I’m rejecting the idea that salt pools somehow need more CYA until somebody eventually figures out exactly why and and back it with both scientific and empirical evidence).
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I think it started with anecdotal evidence that higher CYA seemed to provide better chlorine protection than you would expect from the amount of chlorine bound to CYA. In the Pool Water Chemistry sticky thread, Richard refers to a member from the Poolforum (a lot of the content in that thread, Richard originally posted there and copied it over to TFP - you won't find a member called Aylad on TFP, maybe Janet is here under a different user name):

chem geek said:
1) Some users, most notably Janet (user name Aylad), report that in their non-SWG pools using high levels of CYA shows dramatic improvement in chlorine's staying power. In Janet's case, with a CYA below 60 she found that the FC would go from 7-8 to 2-3 in one day (5 ppm FC per day) while with a CYA of 80-90 the FC would go from 8-9 and take 3 days to go below 5 (about 1.2 ppm FC per day). That is a huge improvement that is wholly inconsistent with the graph.
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Later in that post, Richard lists theories to explain this. The general idea is that CYA doesn't just protect chlorine that is bound to it, but that by absorbing UV light, CYA in the higher water layers also provides additional protection for chlorine (even if not bound to CYA) in the lower water layers.

The main breakthrough came, when Mark (@mas985) did experiments that gave empirical evidence for the better UV-protection at higher CYA levels. A lot of that is happening all along that Pool Water Chemistry sticky thread. It's really worth going all the way through that thread. Richard kept referring to Mark's experiments over the years, for example in 2015 here (with links to Mark's experiments from 2007):

chem geek said:
At any given CYA level, the chlorine loss rate will be a percentage of the FC level. So having 8 ppm FC with 35 ppm CYA will lose about 3 times as much as the minimum 2.6 ppm FC for that CYA level. So losing 4.6 ppm FC is not at all unusual for your situation. If you were trying to maintain something more like 3 ppm FC, then you'd probably be using only 2 ppm FC per day under the same conditions (the factor of 3 may be an over-estimate).

If most of your chlorine loss is from sunlight, then having a higher CYA level even with a proportionally higher FC level will lose less absolute FC per day due to non-linear CYA shielding effects. So you could target 3.8 ppm FC with 50 ppm CYA and lose a little less than targeting 2.6 ppm FC with 35 ppm CYA.

Depending on the specific FC/CYA levels, roughly 97-99% of the FC is bound to CYA and not disinfecting nor preventing algae growth, but fortunately it only takes low levels of active chlorine for these functions. The reason that raising the CYA has less loss is due to two factors. First is that the unbound chlorine, hypochlorous acid and hypochlorite ion, is dependent on the FC/CYA ratio so is the same at 3 ppm FC with 30 ppm CYA as it is with 9 ppm FC with 90 ppm CYA. So the chlorine loss from sunlight from the unbound CYA is the same so long as the FC/CYA ratio is constant and that is also true for the loss from chlorine oxidation of anything it finds to oxidize and from any chlorine outgassing (that's usually a small amount we ignore). So that leaves the chlorine bound to CYA that has virtually no disinfection capability and less than 1/150th the oxidation power, but it does break down in sunlight though more slowly than unbound chlorine.

So you might think that the higher amount of bound chlorine would lose more but we find that it doesn't and speculate that this is due to non-linear CYA shielding effects. That is, the higher CYA level (or possibly Cl-CYA bound chlorine levels) shields lower depths from the UV in sunlight so more than makes up for their higher loss near the surface. Mark did experiments (in this post and this post) showing this effect. My best guess as to the net result is shown in the table in this post where you can see that the total chlorine loss is lower at higher FC and CYA levels with constant FC/CYA ratios.
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Quite recently, Mark did more experiments:

mas985 said:
Many years ago, I did a test of chlorine loss vs CYA level and published the results here:

CYA Testing Update

I thought I would give those who are interested an update on some testing that I have been doing regarding CYA levels and chlorine. First a summary of the testing that I did in this thread. - Running my spa with the SWG at CYA levels from 45-80 ppm showed no change in chlorine production. -...
www.troublefreepool.com www.troublefreepool.com

There were a few issues with the test that I wanted to resolve with some additional testing but never got around to doing it...until now.

This time around, I wanted to use distilled water for dilution to avoid adding anything into the water that might affect the results. Also, for this round, I wanted to use shallow containers (wine tumblers) to determine if the depth of the solution had any impact to the benefits of higher CYA. Also, it wasn't practical to get that much distilled water for buckets so I kept the experiment small.

I started with my own pool water which was at FC level 7.2 ppm with a CYA of 80 ppm. All FC tests were performed using FAS/DPD. One glass had no dilution so had a FC/CYA of 7.2/80. The second glass was diluted 1:1 or FC/CYA of 3.6/40. The third glass was diluted 1:3 or FC/CYA of 1.8/20. Note that FC/CYA ratio is kept constant for all three because of the dilution method. Left in the sun for 2 hours, here are the results:

1:0 FC/CYA 7.2/80 --> FC/CYA 6.8/80 - 0.4 ppm FC Loss
1:1 FC/CYA 3.6/40 --> FC/CYA 2.6/40 - 1.0 ppm FC Loss
1:3 FC/CYA 1.8/20 --> FC/CYA 0.4/20 - 1.4 ppm FC Loss

So as in previous experiments, FC loss decreases with increasing CYA levels although with this test, the benefits seemed to be much greater. This is probably due to the depth of the water as it offers less FC protection due to lower scattering and absorption. The deeper the water, the more UV protection provided by the water so the benefits of CYA are diminished for deeper water.

This is a pretty easy test to perform so I would encourage anyone else to repeat these tests for corroboration.
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I forgot to mention that the effect of better UV protection at higher CYA is not limited to salt water pools. But there is a downside of running higher CYA: Should you ever have to SLAM, you're stuffed with high CYA and you might have to drain.

With an SWG (that is the crucial bit, not the salt water itself), that risk is manageable. With a well dialled in SWG it is easy to make sure that you never drop below the min FC level, and it's worth taking the benefits from running higher CYA.

Without an SWG, all you need is missing to add bleach once due to work commitments, family emergencies, etc, or a batch of old bleach, and your pool is green. The risk of having to SLAM at some point is much higher and outweighs the benefits of higher CYA.
 
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mgtfp said:
I forgot to mention that the effect of better UV protection at higher CYA is not limited to salt water pools. But there is a downside of running higher CYA: Should you ever have to SLAM, you're stuffed with high CYA and you might have to drain.

With an SWG (that is the crucial bit, not the salt water itself), that risk is manageable. With a well dialled in SWG it is easy to make sure that you never drop below the min FC level, and it's worth taking the benefits from running higher CYA.

Without an SWG, all you need is missing to add bleach once due to work commitments, family emergencies, etc, or a batch of old bleach, and your pool is green. The risk of having to SLAM at some point is much higher and outweighs the benefits of higher CYA.
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That’s where I came to it — higher CYA does protect chlorine more efficiemtly, but there’s no free lunch. Just not worth it, at least to me.

I did read the entirety of the chemistry and CYA threads (maybe I’m odd, but I find it interesting) and also saw the experiments that do seem to provide strong evidence of the UV theory. But whatever the mechanism, ultimately at higher CYA levels, higher FC content goes hand in hand. My philosophy for running my pool is to be efficient, but not foolishly so. So, for example, I run my pump / filter 12 hrs / day. I could get away with 8 or 10 hrs. The extra so many hrs cost around $3 / month. The water is always just completely crystal clear. It’s worth it.

Similarly, running my SWG, I could experiment with higher CYA levels and lower commensurate FC (based on the theory of addition of FC throughout the day instead of in large tranches) until something bad happens if I got the FC equivalence “too” low. Not worth it, to me at least. That’s one reason I’m asking all of these questions and fascinated with the answers and in depth discussion of how this all works. We all have different goals, time, motivation, etc., except for the common goal of an economical clean and safe pool that is efficient to maintain. There is more than one way to get there but each way is based on very similar views of the chemistry and explicit acknowledgement of the practicalities, which lead to a diversity of the nitty gritty.
 
I guess we all run our pools the way that works for us. I personally think that the better chlorine protection is worth it. It also means that the difference in chlorine demand between sunny and cloudy days is less pronounced, and my FC doesn't shoot up quite as fast when there is a bad weather spell. And by the time I realise that my CYA is "low", I'm still at 60. Rather than 20.
 
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I may try it yet down the road at some point. Might be a good project towards the end of the season so if I change my mind, the winter water lowering / spring start provides a measure of “free” dilution. The argument that there’s less FC variance due to sun / cloud is very appealing. It’s an interesting topic and I plan to keep reading and thinking on it.

What gives me pause is the sharp drop in ORP as CYA is added, flattening at about 50 ppm. To couple that with basically “ordinary” FC levels because the FC is generated slow and steady is something I need to get my head around. It’s like I just can’t bring myself to intentionally run FC / CYA ratio that low, at least not yet lol.
 
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JamesW said:

Did you know that Vinyl liners contain calcium?

and low calcium causes them to become brittle! Or at least I was just told when I went to pick up some 12% bleach at the pool store. He was told by his "chemist friend" and even drew out the basic formula for vinyl CH=CH2 to show me all the calcium (CH). I tried to explain what a hydrocarbon...
www.troublefreepool.com www.troublefreepool.com
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If I read it right, there is calcium carbonate (likely). We don’t know if inevitable leaching of it does any harm. It doesn’t seem to, at least with historical vinyl liner recipes.

Poking around, it seems to me that UV does the damage (possibly more than chlorine). Topic for another day.
 
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That sounds like a plan. Learn how your pool behaves, and what works best for you.

ORP is tricky with CYA. If you have an automated system based on ORP, then higher CYA levels can be a problem. CYA seems to foul ORP probes.
 
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2. Raw Material Make-Up:

There are 3 major ingredients in the chemical makeup of a vinyl liner:

1. 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.

2. 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.

3. Inert Materials (calcium carbonate – a.k.a. clay) and Stabilizers make up 11%-30% of the total raw material ingredients.
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Two separate manufacturers tested the offshore vinyl and found it had a high percentage of calcium carbonate (between 18 and 20 percent), which Kennedy says adds no value but does reduce cost. In effect, it's chalk filler that's cheaper to use than plasticizers.

The issue with calcium carbonate, Kennedy says, is that it absorbs water, and if it's present in significant amounts, it can cause the types of wrinkling and puckering his field reps had been reporting. The wrinkling issues are only exacerbated when the pool's water is out of balance.

"Just last October one of our manufacturers tested foreign-sourced vinyl and found it expanded by between 18.75 and 25 percent in an exaggerated low-pH environment," he says. "That's compared with only 3.25 percent expansion for domestically produced vinyl with no calcium carbonate."

Another supplier did a battery of head-to-head comparisons between North American and Chinese vinyl on resistance to abrasion, wear, light and other factors. In almost every test, Kennedy says, the imported material proved to be inferior. Often, the differences between the materials were clearly visible.
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www.aquamagazine.com

Getting to the Bottom of Wrinkled Vinyl Pools (Sponsored Content by Tara Manufacturing)

Despite a trouble-free installation, some pool pros are seeing bad wrinkles in their liner installations. Why does this happen? As it turns out, the material might be to blame.
www.aquamagazine.com www.aquamagazine.com

There is a lot that goes into making the vinyl used in pool liners. It has to be strong, flexible and robust enough to stand up to sanitizers, sunlight, organisms and water. If the ingredients that go into the vinyl aren’t of the highest quality, it won’t be able to stand up to demands of the pool environment.

Testing has shown that vinyl produced off-shore can contain a filler ingredient, calcium carbonate. Fillers make the vinyl cheaper to produce but they dilute it as well. That means instead of being flexible and strong, it becomes stiffer and weaker.

Vinyl with high levels of filler content will not fit well and will likely fade or bleach quickly.

Another side effect of using calcium carbonate is its ability to absorb water. As it absorbs water, it expands and forms wrinkles. Once a liner becomes bleached, faded or wrinkled, it can’t be fixed. When you make the investment in a new liner, you want to get what you pay for. Domestically produced vinyl liners from Tara give you that assurance.

Why Choose Domestic Vinyl

Swimming pool company Tara Manufacturing in AL is a leading provider of vinyl swimming pool liners and winter pool safety covers for inground swimming pools.
tarapools.com tarapools.com
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Sometimes calcium carbonate is added to vinyl as a colorant (white) since the alternative, titanium dioxide, is a lot more expensive. So there can be higher levels of CaCO3 due to that. Pure CaCO3 produces a high quality white background, not as good as TiO2, but good enough.
 
Just kind of boiling it all down, looks like calcium carbonate is permissible up to 15% by weight according to the leading manufacturer of vinyl for in ground pool liners. That seems like a lot. I guess based on liner pool owner experience, it doesn’t need it?
 
JamesW said:
View attachment 423660


CGT is North America’s leading manufacturer of premium vinyl for in-ground pool liners.

https://poolsidebycgt.com/about/
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I’m not quite sure how interpret all this. Based on your previous posts you want less then 7%. If it’s from over seas it will be over 7%. If it’s from North America it will be between 0-15% so it might be OK????? Also if it has a white background it is more likely to have calcium carbonate then say a liner with a blue background (backing material) also it probably doesn’t matter really anyway what you keep your CH level at because if the liner was manufactured with a high level of calcium carbonate in it, its not going to be nearly as durable anyway….. did I process all of that correctly? Basically then it seems to me that it makes more sense to try to figure out what liners your better off buying in the first place, and what to be aware of to try to avoid at purchase.
EDIT: less of an issue of CH leaching out of the liner, more of an issue of CH in liner absorbing water?
 
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SoDel said:
Just kind of boiling it all down, looks like calcium carbonate is permissible up to 15% by weight according to the leading manufacturer of vinyl for in ground pool liners. That seems like a lot. I guess based on liner pool owner experience, it doesn’t need it?
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Earlier one of James posts suggested 7%
 

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