Calcium???

[waste]

Hey all,

Can someone please! explain to me why one would still need calcium in a liner pool with either a heater or SWCG?

As long as the water isn't acidic, those vulnerable metal parts shouldn't be in danger, they're made for pool use. I understand about the Langlier index for a 'protective layer of scale' (and the arguments for and against ... so we don't need to go there, or do we?) There has been some argument for having cal in the water of a liner pool, Ben's take was that it wasn't needed, however - our manufacturer says to have > 100 ppm {are they just appeasing the calcium industry or the new NSPI?}, but Ben still said to have cal in the pool with a heater--- ---- What is the calcium supposed to do??

While we're talking about calcium: why is my antacid (for my heartburn) calcium carbonate? (I don't take the aluminum stuff [nor use anti-persperant] because of the 'aluminum/ Altzhimers' corelation) I realize that a baking soda mixture could take care of the heartburn, but it doesn't come in fruit flavors (is the calcium needed to keep them in solid form, as opposed to the bi-carbonate powder?)

The folks I want to hear an answer from know who they are (I almost started a list... but to list the folks here who know chemistry better than I would have required me to double the 'word count' and I would have inadvertantly left out some {I don't want to offend any potential source of info } and I would like any thoughts from the people who know the answer that I couldn't name)

[chem geek]

As far as I am concerned, I don't have a definitive answer for you on whether calcium helps a pool without plaster/gunite/grout. Sources I have looked at regarding water without calcium being more corrosive to metal, even at normal pH above 7.0, are not at all clear about this. I simply cannot find anything that definitively says that the presence of calcium in water will inhibit corrosion EXCEPT that a saturation level of calcium carbonate MAY form an inhibiting layer on metal. But other sources say forming such a layer is virtually impossible since it is uneven and if saturation is enough to start significant formation (probably a saturation index above +1.0), then it is enough to continue buildup (which is not good). Clearly in a heater, you don't want a thick layer of calcium carbonate since that reduces heat transfer (calcium carbonate does not conduct heat well) and would eventually burn out the heater. This is why Ben generally recommends being slightly corrosive in water balance since the higher temperature of the heater will shift that balance closer to neutral (neither corrosive nor scaling). The Langelier index was originally developed for boilers so apparently it did help in that environment so in theory should help with pool heaters, but that is at saturation levels.

In an SWCG pool there is a higher level of salt, though that can obviously occur in a non-SWCG pool where additional salt has been added or where a lot of liquid chlorine has been used without splash-out or backwash. Here again it is not at all clear whether calcium inhibits the greater corrosion rates from the higher salt levels and it's also not known exactly how much higher the corrosion rates from higher salt levels actually are. There is no question that the higher salt means higher conductivity so greater potential for electrolytic corrosion (including galvanic corrosion from dissimilar metals touching or electrically connected), but I can't find anything that says that calcium levels inhibit this (except the general discussion I gave above about saturated calcium carbonate levels).

In other words, I don't know, but let's look at an interesting situation. It used to be that water systems used chlorine for sanitation and the water flowing through homes was (and still is) typically in copper pipes. Typical numbers for Total Hardness are around 70 ppm in our metropolitan area (and a Calcium Hardness of around 50 ppm). I don't recall hearing about or reading about horrible corrosion issues in many copper piping systems in people's homes. The residual chlorine levels were relatively low, but there was no CYA so in actual fact the levels were higher than found in pools in terms of disinfecting chlorine level. Today, monochloramine is used and though at higher levels, it's a far weaker oxidizer so far less corrosive to metal.

The reality is that the chlorine in pools is what corrodes metal faster than anything else -- it has a much higher oxidation potential than oxygen in the water, even accounting for actual disinfecting chlorine concentration. We know that stainless steel is also susceptible to higher chloride levels (e.g. in SWG pools) for faster corrosion, but don't know how much faster at various chloride levels.

Your antacid is calcium carbonate because this is alkaline and helps counteract the excess acid. It's not just a buffer, but a base. There is no such thing as calcium bicarbonate (except in solution) and you don't take lots of sodium bicarbonate because the extra sodium isn't good for you (it's the sodium that is of concern in limiting one's "salt" intake). Nevertheless, there are antacids on the market that contain any of the following, sometimes in combination (see this link for more details):

Calcium Carbonate -- a base (alkaline) and a pH buffer
Magnesium Carbonate -- a base (alkaline) and a pH buffer
Magnesium Hydroxide -- a base (alkaline)
Magnesium Oxide -- forms Magnesium Hydroxide in water -- a base (alkaline)
Sodium Bicarbonate -- a pH buffer
Aluminum Hydroxide -- a base (alkaline)
Dihydroxyaluminum Sodium Carbonate -- a base (alkaline) and a pH buffer
Dihydroxyaluminum Aminoacetate -- a base (alkaline)

Additional items may be added for other purposes such as reducing gas (e.g. simethicone) but are not strictly antacids.

Richard

[waterbear]

I have been researching this also and have found nothing difinative in whether calcium is needed in a vinyl pool but there is some evidence that it MIGHT be needed in a fiberglass pool to help prevent colbalt leaching from the gelcoat. I have also seen some suggestions that calcium can help contribute to pH stability in conjuction with the TA but the chemistry was rather muddled so I am not at all sure it is valid.
EDIT: If there is a manufacturer's warrenty involved then I would add the calcium to the level they recommend to maintain the warrenty. It's not going to hurt anything.

As far as anti acids go---they neutalize 37 times their weight in excess stomach acid!

[cleancloths]

I recall seeing a report from a vinyl manufacturer that explained that calcium in the water is important because the liner contains calcium fillers and it will tend to leach out of the plastic if there is none in the water. That said, I have never added calcium to my pool in the 8 years I have had it and can see no harm to the liner, metal or heatpump.

[waste]

Thanks for the responses!! (I'm trying not to be one of those ' I got the answer and you won't hear from me until the next problem' posters

[AnnaK]

My test strips (AquaChem) test total hardness with a value at 0 presently. I just came back from Leslie's. Their test says 80 ppm calcium hardness and he wants me to add 18 (!) pounds of Hardness Plus. I said, I thought hardness didn't matter so much in a vinyl-lined AG pool and he said, oh yes it does because the water "wants to be hard and will leech what it can out of your liner, and stretch it".

But then, reading here on the Forum, I'm left with the impression that I really don't have to worry about hardness as long as the rest of my values are balanced, which they are.

If it were your pool, would you add Ca?