Calcium for metal

[RavenNS]

Hi,
I've been learning a lot here the last few weeks, particularly interested in the Calcium debate.
Everytime I get a water test at a store, they tell me to add more Calcium

This last time was the smallest amount "needed"... only another 16KG
I told them that I was not buying it ( both literally & figurtively..lol)
I told them that I had read that calcium wasn't really necessary for a vinyl pool...
they told me that it's not the pool that needs it but rather all the metal components in the system... ( )

I would think that having a lot of calcium on metal would be a bad thing?
( isn't that called scaling?)

So: What's the deal here?
Does a pool pump need calcium to function well?
I also have a heat pump, but don't remember seeing anything about calcium in the manual ( although PH was mentioned)


.......
test scores:
TA : 110
PH : 7.2
CYA: 40
total hardness (calcium): 130 ( they said it should be at least 200 to 350)
TC : 1.7
FC : 1.7
---------------
Thanks for your help,
G :-)
------
VITALS:
aprox: 140000 litres, jacuzzi Vinyl inground Lazy "L"
Sum5 Summit Heat Pump 115000 BTU
Zeobrite running in jacuzzi 25 sand filter
3/4 hp pump ( don't know the brand)
pool devil pro
kreepy krauly
Dolphin w/remote ( in shipping, scheduled to arrive next week)
Beachcomber Hot Tub ( #578)
lifestyles hot tub (yuck)

[RavenNS]

just bringing this thread forward becuase no one answered my question yet...
Is calcium needed for the metal components of pool equipment( to function better) ?

[GraceByDesign]

Cal is required for heaters, but it appears to be a level lower than you already have, so you should not need more. Read here

[ubalr1]

.......
total hardness (calcium): 130 ( they said it should be at least 200 to 350)

It is my understanding that Total Hardness is more than just calcium. Total Hardness as measured at the pool store refers to the total mineral content of the water. That would be calcium, magnesium, iron, manganese, and more. Have you tested specifically for calcium hardness?

[RavenNS]

"Total Hardness (calcium)" was how it was written from the Pool Store test...
so I guess that was a calcium only test.

My test strip for T.H. showed it at over 350 but under 500 ( that, I would guess would include the remaining metals)

My TDS was a bit over 800 ( I had them check that, out of curiousity, because they didn't test for metals)

to date we have added over 100KG of calcium this year which seems really high to me,
( but what do I know about it? newbie...lol), for a 140000 Liters ;
this is not fresh water either, it hasn't been "changed" in at least 8 years ( possibly a few years longer).

thanks for your help :-)

[DavidD]

The short answer is no, you do not need calcium. Chances are your pool store is just following protocol. You know, the selling you more stuff protocol...

I wouldn't add any more. And you should ditch the "guess" strips.......

Dave

[RavenNS]

Thanks for the help guys

& yes, i would ditch the "guess" strips, but Ben doesn't sell to Canada...lol

Actually there were two different reagent type kits in the "pool house" of this place that we bought this last winter; unfortunately, I'm apparently too "stupid" to figure out how to use them.
The directions didn't make any sense to me. Even watching the Pool store people do these types of tests still had me confused about what i was really looking for in each test... ( I mean yeah if it's just colour changing, I can do that... but if it's watching how the "dots" spread out or not & how many drops needed before..? whatever?..... I don't get it...lol)

So I have actually 5 different types of strips... we have two hot tubs as well, so I have to keep on it.
And I also have an electronic CL & PH meter. I know those aren't supposed to be that acurate either, but i do comparrisons with all the strips & so far everything seems to be matching up.
I also do weekly water tests through our Hot Tub store ( rather, the store that we use; it's not "my" store, although I'd love to work there)... they're computerized for testing.
I also am doing monthly water tests at another pool store, just to compare test between the two stores.

My conclusion is that nothing is 100% acurate, but I can get a pretty good picture between all of these different tests

[chem geek]

Calcium, along with carbonate (alkalinity) and appropriate pH, is needed when you have a plaster pool or other grout in order to prevent them from corroding (dissolving) into the pool water. A vinyl pool does not need calcium for this purpose.

The belief that calcium is needed for heaters or for other metal surfaces is that in certain environments that can be normally corrosive to metal, having a "protective" layer of calcium carbonate scale can help to protect the metal from corroding. However, corrosion of metal is not at all the same thing as corrosion (dissolving) of plaster. The fact that you do not have calcium does not make your metal corrode any faster -- only lower pH, higher temperature, increased dissolved oxygen or oxidizing chlorine (HOCl) levels, and higher conductivity (higher salt or TDS) can cause that. In practice, if the pH stays above 7.0, then corrosion effectively does not occur (in pool water; sea water is another matter, but that's due to higher levels of dissolved oxygen and salt and even then it is iron that normally corrodes well before copper).

It is not clear whether you can realistically maintain pool water in a slightly scaling state (for calcium carbonate) to have this deposit on metal pipe surfaces (typically copper) in your pool heater and to do so as a thin film that is enough to prevent corrosion and yet does not continually build up to the point of blocking water flow. In heat exchangers this balance between corrosion vs. scaling is a serious issue, but in a pool it is much less clear that calcium carbonate water balance is important for anything except plaster/grout pools and even then it appears that you have to stray very far away from ideal balance before you run into problems.

So, bottom line, for your vinyl pool, don't worry about calcium. If you are worried about corrosion of metals, then keep your pool's pH in the normal range (well above 7.0) and don't use Tri-Chlor tablets for your regular chlorine source as these are highly acidic.

Richard

[mbar]

Thanks Richard for clearing this up. I am still hearing different takes on if you should use calcium in a fiberglass pool. Now I can see that it really isn't necessary.

[chem geek]

Thanks Richard for clearing this up. I am still hearing different takes on if you should use calcium in a fiberglass pool. Now I can see that it really isn't necessary.

Marie,

If anyone has either real-world experience with metal corrosion due to low or no calcium (as opposed to low pH) or if they are aware of scientific reasons why calcium is needed, I'd like to hear about it. Please don't take my word for it just because the science seems to indicate that it isn't a problem. I have been wrong before and will no doubt be wrong again so if real-world experience contradicts my beliefs, I certainly want to know about it. I'm just relating my understanding as it is at this time.

Thanks,
Richard

P.S. My own personal experience with metal corrosion in my own pool (we have bars in the pool just under the water line) is that the only place corrosion occurred was near where the floater with Tri-Chlor tablets had been and that I had the pool pump running 8-10 hours/day (i.e. not 24/7). I also had a thermometer corrode when I put Tri-Chlor in my skimmer. So localized low pH conditions can certainly cause corrosion. Needless to say, I don't use Tri-Chlor anymore and all of this occurred long before I got involved with this forum.