What is my Shock Target level

[NoskoSteve]

New owner. Read a bunch on the site. Have had enough chemistry to know how to calculate concentrations and much of your info makes sense to a retired Engineer.

Above Ground Intex, 4400 gal. Pool on order.

I'm on City water and a local pool-centric hardware store tested my UN-softened water and only reported that it has "a little iron", which I knew from past waters oftener analyses.

1 - Is it actually necessary to always shock when filling pool first time of the year from city water?
1a - My city water most likely has a slight chlorine smell (it used to), but we wouldn't be able to notice it any more, we're so used to it. I didn't realize that it is CC that smells, not FC…so the chlorine ion does not smell? It only smells when combined with something that it 'killed', or in some inorganic compound (laundry bleach is a hypochlorate)? NaCl doesn't smell and it sounds like it could be called "CC".


2 - NEVER MIND. ID10T Error. I just read the table for real... I have my Shock level...


3 - Also, I assume when you have just numbers for thing like FC, CC etc, it is assumed to be ppm, no?
The Pool School Chlorine / CYA Chart just has numbers. It'd be nice to have something to indicate that all numbers are in ppm or whatever they are. As an engineer it's important to always see what units are, especially when you're getting into a new area, as your Pool School is targeted to newbies.

4 - One of the store folks recommended some stuff "to remove minerals". Knowing some people travel half way around the world to soak in mineral water, I asked *how* it removed them and she said they fall to the bottom. Ok, so it precipitates them out. When I asked why would I care, she said because they can turn color - iron red, etc. DO I care? What would cause a color change, (oxidation of the iron?)

Nuf' for now.
Regards, Steve N

 

[Richard320]

Let's see.

1) No, you don't need top shock initially, there shouldn't be any algae in drinking water
1a) Many municipal water systems use chloramines to prevent corrosion or something. It will dissipate when you get some sunlight and some bleach.
2) Okay
3) Yes, ppm.
4) Depending on the minerals, you can get staining or discolored water or calcium scale. I'm willing to bet what they're trying to push is phosphate remover, which is unnecessary. Or a metal sequestrant, which may be necessary if you get stains.

 

[BoDarville]

Richard beat me to it, but since I have this queued up...

1 - Is it actually necessary to always shock when filling pool first time of the year from city water?

After you fill your pool, run a complete set of tests. Using your test results, use the Pool-Calculator program (click link in my sig), determine the correct amounts of chlorine, CYA, acid (to lower pH) or Washing Soda, Soda Ash, or Borax (to raise pH) and dose as instructed. Then run an OCLT (see link in my sig). If you fail the OCLT, then follow the Shock process. Appropriate doses of chlorine to "shock" the pool can also be found using the Pool-Calculator program or the Chlorine/CYA Chart. If you need to shock, lower the pH to around 7.2 before beginning the shock process.

3 - Also, I assume when you have just numbers for thing like FC, CC etc, it is assumed to be ppm, no?
The Pool School Chlorine / CYA Chart just has numbers. It'd be nice to have something to indicate that all numbers are in ppm or whatever they are. As an engineer it's important to always see what units are, especially when you're getting into a new area, as your Pool School is targeted to newbies.

Numbers for FC, CC, and the Pool School Chlorine/CYA Chart are in ppm

As for # 4, what Richard said.

 

[NoskoSteve]

OK thanks. Sounds reasonable.

Folloup:
What is the mechanism by which the sun depleats the chlorene? It has to combine with something if it doesn't evaporate and UV is probably the driver. I can understand that there can be *some* evaporation, but what is the chemical reaction, if any? Seems it must be turning FC into some form of CC? (CC in general, has to be a chlorene compound, like with sodium, calcium, magnesium, etc as well as from any organics)
Steve

 

[Smykowski]

UV is probably the driver.

Exactly right. Chlorine depletion during daytime is from UV radiation breaking up the HOCl.

The other ways chlorine is consumed is through oxidation (of usually nitrogen compounds) which leads to combined chlorines, and sanitation of living organics (which might result in CCs, but not always)

 

[techguy]

Also be aware that the most common errors in pool maintenance are PEBCAK errors.

 

[NoskoSteve]

Ahhh. So the free Chlorine isn't chlorine ions, but HOCl. Interesting. Gotta do more homework with my Chem Engineer son. (;-)
I also gotta' learn how to spell chloreen.
Thanks.

 

[UnderWaterVanya]

Ahhh. So the free Chlorine isn't chlorine ions, but HOCl. Interesting. Gotta do more homework with my Chem Engineer son. (;-)
I also gotta' learn how to spell chloreen.
Thanks.

Wait a sec... isn't HOCL just a bunch of H+ and OCL- ions loosely associated with one another waiting for an excuse to go hang out with someone else more attractive to each of them?

From Wiki...
In aqueous solution, hypochlorous acid partially dissociates into the anion hypochlorite OCl?:

HClO OCl? + H+
Salts of hypochlorous acid are called hypochlorites. One of the best-known hypochlorites is NaClO, the active ingredient in bleach.

HClO is a stronger oxidant than chlorine under standard conditions.

Cl 2?HClO(aq) + 2?H+ + 2?e? Cl2(g) + 2?H2O E = +1.63 V

 

[techguy]

Where's ChemGeek... we really need a ChemGeek bat-signal.

 

[Smykowski]

When I first found this forum, the most valuable treasure (besides the $$$ savings of not getting pool stored any more) was the "how and why" chemistry that I got, mostly from Chem Geek. Here are two good posts, but beware, you'll be jumping so far into the deep end you won't be able to see the shore anymore....

chloramines-and-fc-cya-t10257.html

pool-water-chemistry-t628.html

 

[NoskoSteve]

I didn't mean to start chemistry class (so to speak). (;-)

Chem Engineer Son sent me this, in part Regarding: "... hypochlorite solutions, … and compounds like … "dichlor", …"trichlor". These compounds ... When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule forming hypochlorous acid (HOCl), which acts as a general biocide, killing germs, micro-organisms, algae, and so on.[45][46]..." (From Wiki.)
I'm gonna' guess there may be variations to what happens, but this satisfies my curiosity.

Steve
P.S. Ir's a good thing my pool is taking a few days longer than expected to get here; more time to absorb what I need to do and figure how serious I'll actually get.

Thanks for your help getting brain in gear. I knew it would be a bit more complex/work, but a few moon-light swims with wife and it won't matter any more....