Calcium Hardness and pH/Alkalinity.

[seilsel]

I called Taylor today to finally ask them why they recommended a minimum CH level of 150ppm for a vinyl pool. I spoke to two people before finally being directed to a third. He said that even if the calcium didn't come from the vinyl, the water would try to pull it from somewhere. I said that most everything is PVC and fiberglass - in that case, why the calcium? If water is getting onto the pump motor, you're in trouble regardless of the calcium levels.

His two responses were that it could pull calcium from behind the liner (what?) and that low calcium levels made it difficult to balance pH and Alkalinity. Is there any truth to this? If not, the misconceptions must come from somewhere - does anyone know where?

Thanks any who take the time to answer, as always.

 

[dmanb2b]

pulling calcium from behind the liner wow

The only argument I have ever heard for maintaining a certain CH level in a vinyl lined pool is due to warranty requirements with the equipment attached to the pool, iff applicable, like heater etc. Other than that I would ask that rep for his source.

 

[chem geek]

Low calcium levels making it difficult to balance pH and Alkalinity??? I think they may mean that if you wanted to get to a zero saturation index, then a low CH would require an awfully high TA and pH combination, but that isn't the point. The question is whether a low saturation index matters in a vinyl pool. I haven't heard any reasoning from them (from what you wrote). I'm surprised they didn't use the argument about protecting against metal corrosion (which is debatable and unlikely -- see this link).

 

[mas985]

On this page they mention that low CH can have an effect on grout as well as the deck concrete. So even if you have a vinyl pool, there could be other things that are susceptible to calcium corrosion although it would depend on the exposure of those surfaces to the pool water.

 

[chem geek]

Yes, we usually say something like "plaster or any exposed grout in tile". I hadn't considered deck concrete, though rain water wouldn't be good for such concrete either so similar sealing precautions are probably needed in that case.

 

[PaulR]

In a hot tub, having some CH helps reduce foaming. Pools don't usually have the massive aeration of a hot tub though.
--paulr

 

[StuartPool]

http://www.swimuniversity.com/water-che ... -pool.html

Web page ad

 

[dmanb2b]

yeah...notice the recommend products...I do know but I doubt soft water speeds up the breakdown process of vinyl.

 

[JasonLion]

Low calcium levels do not bother vinyl pools at all. Concrete, plaster, tile, pebble, quartz, gunite, grout, natural stone surfaces, and to some extent fiberglass can all be damaged by low calcium levels, but vinyl is just fine.

 

[chem geek]

http://www.swimuniversity.com/water-chemistry/why-you-should-add-calcium-hardness-swimming-pool.html

The reasoning they give for adding calcium to a vinyl pool is the following:

What this chemical does is harden the water so that your water doesn't penetrate the walls of your pool and slowly eat away at your vinyl liner or concrete walls. Soft water is known to do this and by adding this chemical you are preventing that from happening.

Calcium hardens the water so that it doesn't penetrate the walls of the pool and eat away at the vinyl liner? This makes no sense whatsoever. Now if you had a leak in the vinyl, then if the water was exposed to concrete it could slowly dissolve the concrete, but again that requires a leak in the vinyl liner. Also, unless the leak was rather large, any dissolving of the concrete would quickly saturate the water near that concrete and the dissolving would stop. It's only if there were good water circulation with the rest of the pool where there could be a problem.

 

[mariane]

To resurface (pun intended) this thread.
At the pool store, I was told "Low calcium would cause wrinkling to the vinyl liner." :blah:
If there any merit to that? I do notice wrinkles but that could be due to hypersensitivity on my part, being hyper vigilant the do the right thing, and to keep the pool water perfectly balanced.
I have an above ground metal pool with vinyl liner.

Thanks for clarifying this.
Mariane

 

[JasonLion]

Thousands of low CH pools, over many years, no wrinkling.

Low PH can cause problems for vinyl.

 

[mariane]

Thanks Jason.
Just as I thought. Words from the pool store :blah: :lol:
(pH has always been in range.)

mariane

 

[Bama Rambler]

Almost zero CH here and no problems so far.

 

[Stuamurr]

I dont really want to re-hash an old subject, but have been reading this thread with interest, I note most if the noteworthy contributors to this site will claim that low or zero CH levels in vinyl pools is not of concern.

Chem Geek linked an excellent discussion about the relevance of the LSI, with some scientists opinioning that LSI was only really of worth for detecting positive values in the scale forming range. Whilst a consensusseemed to be that which I understood that the LSI be a reasonable indication of wether water would have tendancy to be scale forming, neutral or errosive/corrosive.

My understanding about errosive and corrosiveness is at minimal levels it will attempt to devour calcium through grout/tiles etc, which is not an issue in liner pools, however at higher levels will corrode or errode metal, particularly copper.

My area of concern is that advice given that not correcting CH levels in vinyl pools, because there is nothing to eat, is or may be innacurate, as low LSI would pose a risk to the corrosion of heat exchanger piping, metal impellers, and SWG where the water passing through these equipment is suggestive that they are corrosive/erosive.

I would be obliged if some could comment on this, I frequently see the claims that in vinyl pools that there "is no concrete/grout to eat" so therefore no reason to add calcium, but there never seems to be discussion or re-inforcement on the matter of plant equipment.

The matter in vinyl pools, and my understanding that if a water is erosive and or corrosive (putting the LSI indication aside) that those erosive waters would therefore seek out to devour primarily the copper in the heat exchanger and this would actually be exaserbated by the lack of other available calciums or metals available.

Regards
Stuart

 

[Bama Rambler]

Here's an interesting read about that from the Water Quality Association. Aoocrding to them it's not corrosive.

 

[JasonLion]

This whole confusion has to do with imprecise word usage. Low CSI/LSI will "corrode" plaster surfaces, but will not have any effect on metal. There is a long history of people misinterpreting "corrosive" as applying to metal, but it really doesn't in this context.

 

[onBalance]

As Jason mentions, there is a difference between being "corrosive" to metals VERSUS being "aggressive" towards calcium carbonate (cement based materials). One can have water that is aggressive (negative LSI) towards calcium, but not be corrosive to metals. Conversely, one can have water that is scale forming (non-aggressive or positive LSI), but at the same time, that water can be corrosive to metals. That is why there are other indexes like the Larsen, Riddick, and Singley, which have more to do with the "corrosivity" of water towards metals. However, high salt content does contribute towards the "corrosiveness" of water.

 

[PoolGuyNJ]

Water is also called the universal solvent.

Calcium is one of the primary ingredients for cementatious products. Its what make everything bind together.

Water tends to dissolve calcium from these surfaces causing pitting, in varying amounts based on several factors. These factors are temp, pH, alk, and the amount of calcium is solution.

For a swimming pool at swimming temps, we can make the water less likely to draw calcium by ensuring the alk, pH, and calcium hardness levels are kept up. By changing some the levels, we can make the water want to draw calcium from the plaster used, be it plain or colored plaster, Diamond Brite, or a high aggregate like Pebble Tec. The less cement exposed, the longer the finish can withstand aggressive water. There is a limit where instead of drawing calcium from the finish, calcium will precipitate and stick to a cementatious surface, forming scale. A positive CSI level indicates scale can form. Keeping it ever so slightly negative will prevent scale and the water's ability to reduce the calcium content in cementatious surface is significantly reduced to negligible. High aggregate finishes exposes the aggregate, not the cements holding the aggregate.

Plaster uses marble dust, by the way. Water will tend to dissolve the calcium there too if the CSI to too negative. This forms pitting and makes a surface rough. You can only sand it and polish it when this happens and that has limits too.

Muriatic acid washes, because the pH is so low and that lowers the CSI, tend to eat the calcium.

Scale often forms most visibly on tile. The tile is exposed to the sun and is often a bit warmer. When water gets warm, it will hold less calcium in solution. Cold water actually holds more than warm water.

Scott

 

[chem geek]

As often happens with simplified statistics, if one simply looks at a bunch of different water types and looks at metal corrosion rates, one may find that lower LSI has higher corrosion rates. But if one looks more closely, one finds that it's mostly low pH that is the primary factor. The next important factors are the conductivity of the water and the presence of oxidizers including oxygen. After that, things get more subtle with various ions being either corrosion enhancers or corrosion inhibitors. And there are specific issues for certain ions (such as chloride) with certain metals (stainless steel).

The lack of calcium is not corrosive. It is the presence of calcium and carbonate in saturation that can form a protective film that can inhibit metal corrosion, but it's very tricky for such films to form consistently. Also, I should note that using Cyanuric Acid (CYA) in the water reduces corrosion rates significantly compared to having chlorine without CYA since it is the active chlorine (hypochlorous acid) level that is the primary oxidizer for corrosion.

My tap water has an LSI of around -0.7 mostly because the Calcium Hardness (CH) is 55 ppm. Phosphates at around 300-500 ppb are added to the water by the water district as a corrosion inhibitor, but the pH is 7.7 so corrosion rates would be low regardless. Also, having the water be chlorinated (or chloraminated) helps prevent biofilm formation by killing bacteria before they can form biofilms. Biofilms can cause corrosion since the metabolic processes can be acidic.