Newbie: To shock or not to shock... That is the question

We are in the process of building our first pool (23k gallon, IG, SWCG, gunite) and I have been doing a lot of reading here and on PoolSolutions and I am a little confused about the need to 'shock'. One local pool dealer says that with the SWCG, I shouldn't ever need to shock. Another indicated I would still need to shock. On PoolSolutions it indicates:
What's essential -- for concrete pools:
Chlorine must stay above 0.5 PPM --- always, always, ALWAYS
Chlorine must go above 5.0 every week or so. (Shocking)
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But later on that page says:
What's desirable -- for concrete pools
Chlorine should stay above 1.0 PPM
pH should stay between 7.2 and 8.0
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So when I read that, am I to assume that if I keep my Chlorine above 1.0 PPM all the time, I shouldn't need to shock unless something else happens (like algea)? Or, should I still plan on bumping up the Chlorine once a week to 5.0? If I do need to bump up the Chlorine every week or so, how long should it stay above 5.0, and can that be done with the SWCG or should I just use bleach?

Thanks so much for any guidance you can provide.

I've never shocked my pool just for the sake of driving the chlorine up or as part of my regular maintenance. If you keep your FC concentration at a level appropriate to the amount of stabilizer you have there is no need to raise the chlorine to shock level. That really only has to be done if, for some reason, you get an algae bloom. Should that happen, use bleach.

For a point of reference, I keep my stabilizer (CYA) at 50 ppm and the FC level at between 3 and 4 ppm.

I've asked Ben to check the Pool Solutions pages to see about the possible conflicting information.

Actually, that's very old page that hasn't been accessible for years, until about a month ago.

It needs to be updated to reflect the data in the "Best Guess" chart which I developed about 4 years after that page -- you should use that page instead. The info on the page really is only accurate for low levels of stabilizer.

I just looked for the page, but Google can't find it because it's in a section I don't allow Google to see (till I've finished the updates). I remember it, but I can't remember what the page is called. I hope to get back to working on those pages next week . . . but we'll see.

Ben

Here's some updated info as best I remember it from the guys who work on SWCGs.

1) Pool maintenance is pool maintenance. The SWCG makes things easier and SOME recommended numbers change, but all in all it's the same.
2) Shocking is what you do when you have a problem or suspect you have a problem. Most systems can gen higher levels of chlorine, but (and I'm guessing here), not enough to clean up a major algae bloom.
3) Bleach/liquid chlorine is the ideal adjunct method for adding chlorine. Bleach is made from salt-water, ie brine, and you had to add salt to the pool for the SWCG to work.
4) Manufacturers generally prefer higher levels of stabilizer (CYA) than expected. 70-80ppm is pretty normal.
5) according to Chem_Geek, our resident chemistry geek (get it?) you need to keep FC at 5% of cya, so that's 3ppm when CYA=60ppm and 4ppm when CYA=80. It's also much lower than the Best Guess table, but the SWCG puts a steady flow of chlorine into the water.
6) According to our other pros, a low Total Alkalinity works very well. 60-80ppm is what they tell us, far lower than the 80/90 to 120/130. I'm guessing it has to do with the tendency many SWCGs have to raise pH. A lower T/A may buffer that.
7) for reasons I don't understand, even a vinyl pool may need Calcium with a SWCG.

Hope this helps.

Carl

So, I am to assume that I only need to shock my pool when I have a problem... correct? I don't need to shock it on a regular basis just because some pool dealer told me I needed to, is that correct? Sorry for the repeated question... I just want to make sure I completely understand the purpose for shocking a pool, and the regularity that it needs to be done.

you do not need to shock, unless you have a problem- I did not shock at all last year, after completed opening...
Shocking is to kill an algae bloom, or oxidize CC, or oxidize/sanitize organics; if you do not have a high swimmer load, and maintain FC at levels indicated by best guess chart, you won't have to shock either.
Happy Swimming!

You only need to shock if you let your chlorine level drop below the range that you are supposed to keep it in based on your CYA level (see Best Guess chart below in my signature), or if you have a really big swimmer load, or if you have a CC reading above 0.5. I also sometimes shock if I have a big storm that throws a lot of debris in my pool. Other than that, you don't really need to shock. I rarely shock my pool because I maintain my chemistry where it needs to be. I'm guessing other than at start-up, I probably don't shock my pool more than twice a summer and maybe not even twice. Of course pool stores tell you to shock weekly. They want your money!

Quote:

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Originally Posted by Watermom

You only need to shock if you let your chlorine level drop below the range that you are supposed to keep it in based on your CYA level (see Best Guess chart below in my signature), or if you have a really big swimmer load, or if you have a CC reading above 0.5. I also sometimes shock if I have a big storm that throws a lot of debris in my pool. Other than that, you don't really need to shock. I rarely shock my pool because I maintain my chemistry where it needs to be. I'm guessing other than at start-up, I probably don't shock my pool more than twice a summer and maybe not even twice. Of course pool stores tell you to shock weekly. They want your money!

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+1 for me exactly. I didn't go to shock levels at all last year except on opening. I will run the pool at the highest end of the operating level or even a little higher after heavy bather loads, storms, heat waves or other weirdness. That has been adequate.

According to Taylor you want to achieve Breakpoint chlorination (10 x the CC level) any time your CC reaches .2ppm I have been trying this at .5ppm and it seems to be working ok. I really don't think of it as "shocking" the pool when I'm only raising it to say 7ppm when I have a cc of .5 but I guess technically it is. My normal target range is 5-9 so you see I can achieve Breakpoint as a matter of my normal maintenance. Just another way of saying the same thing as the others perhaps.

The 10x rule is wrong when applied to CC. The rule originally came from the amount of chlorine needed to oxidize ammonia where the molar ratio is 3 chlorine to 2 ammonia. However, chlorine is measured in ppm Cl2 units while ammonia is measured in ppm N units and there is a factor of 5.06 difference between these units. So the ratio in chlorine and ammonia units becomes (3/2)*5.06 = 7.59 where side reactions and getting over the dichloramine hump has actual quantities required be in the 8-10 range and that's where the 10x rule was born for the chlorine oxidation of ammonia in their respective units.

CC as monochloramine already has 1 of the 1.5 chlorine needed to oxidize it and CC is measured in chlorine ppm Cl2 units and not in ammonia ppm N units so there is no factor of 5. So 1 ppm CC only needs somewhere in the 0.5 to 0.7 ppm FC amount to get fully oxidized. Now there are other forms of CC including monochlorourea that need more chlorine, but still on the order of 2-3x the CC level. Besides, breakpoint chlorination is continuous so long as there is ANY measurable FC in the water and nothing gets "stuck" if you don't use enough FC -- you simply add more and it picks up where it left off (more or less).

If you are measuring 0.5 ppm CC using a 10 ml sample size in your FAS-DPD chlorine test, then that is really <= 0.5 ppm and you should use a 25 ml sample size instead to see if it's really <= 0.2 ppm which is more likely.

Now, all that said, it is true that a higher active chlorine level (FC/CYA ratio) will oxidize CC faster, but just don't think there is anything magical or special about "10x".