To shock or not to shock

[tokmom]

Is shocking necessary on a weekly basis if things seem to be ok? Our pool is covered with a solar cover as the pool for the next week or two will not be used due to rain and cooler weather.
The water is pretty clear, and we have been running the robot and cleaning the sides every other day, and our heat pump is set at 75 and the pump is running 24/7. We also have trichlor tabs in the floater.

Testing shows with the Taylor 2006

CL 5
FC 3
PH 7.4
Hardness 100
TA 120
CYA 30-50

It has been a week since the last shock and I did so because we had pretty heavy use one day.

Thoughts and thanks in advance!

[Watermom]

It is not necessary to shock a pool every week. The only time you really need to shock is when you are having issues of some sort --- cloudy water, CC reading over 0.5 or after a really heavy bather load or if a heavy rain drops a lot of debris into the pool.

If your chlorine readings are correct, (I am assuming that by CL you mean TC?), then you have a CC reading of 2; thus you need to shock the pool. (FC+CC=TC)

All your other numbers look fine. If your CYA is 30, then you can use the trichlor tabs for awhile but if your CYA is 50, then I would not use them anymore because they will continue to add CYA and 50 is about as much as you want for most pools.

[tokmom]

Duh..yeah that is what I meant was TC (blushing) That is what I get for typing while on Nyquil, lol.
Can you explain or is there a link about the arriving at those numbers? FC+CC=TC? This confuses me.

Will do on the CYA. It's been raining buckets here. Does that dilute the CYA? Husband says it's closer to 30 according the the test.

Oh one more thing that confuses us and maybe understanding the FC+CC=TC will help us on they 'why' but we thought if the numbers were ok that we didn't need to shock. Won't that raise the chlorine too much?

Again, thank you for all your help. I have learned so much, but obviously have far to go, lol.

[Watermom]

Rain will dilute all levels some but not significantly.

You are right that if your numbers are ok you usually don't need to shock. But, your numbers are not ok. You have a CC reading of 2 and you want it to be 0. The way to lower the CC is to shock the pool. How high to shock depends on what your CYA level is. If you haven't yet done so, please read the Best Guess Chlorine Chart in my signature below.

So what you need to do is to shock the pool up to a chlorine level of 15ppm. In your pool, each gallon of plain, unscented 6% bleach (generic is fine; most of us use generic Walmart bleach) will add about 3.7ppm of bleach. Use that as a reference to help you figure out how much bleach to add each time you test. You'll want to keep the chlorine level at about 15 until you can go from sundown one evening to within two hours of sunrise the next day without losing more than 1ppm of chlorine overnight and you have a CC reading no higher than 0.5. At that point, I would suggest keeping the chlorine high for one additional day and then let it drift down and keep it between 3-6 all the time.
(Once you get past this, I'd suggest bumping your CYA up a little to get it up to about 50. You can use trichlor pucks for a little while and monitor your CYA level every couple of weeks.)

Hope this helps.

EDIT to add a link for you to read which may be helpful.

http://www.poolforum.com/pf2/showthread.php?15189-Abbreviations

[tokmom]

Thank you for your response. We have a bottle of liquid Walmart version of pool chlorine that I think is 12%. As for the Best Guess Chart, I have studied the chart and I thought I understood it. However, I guess I didn't, because were were always in the green.

We did shock this afternoon, before reading your response about adding bleach. Now are numbers are this, and there seems to be another dilemma. The CYA level. I assumed when my husband gave me numbers that he was using Taylor. What he has been using as been strips. The strips show 30-50 and the Taylor shows ZERO. He says he has never been able to get the dot to disappear... So which do we believe?? Do we add stabilizer? This would explain the lower chlorine levels, right?
Husband says on the strips the Chlorine and FC were 10. Such a difference in strips vs Taylor!

Numbers after shocking:

FC 12
CC 0.5
Hardness 130
PH 7.4
TA 160 (do I need to drop this? Seems rather high)
CYA zero...

Again, thanks for your help. I feel like a broken record, but you all amaze me with your water science. I'm a nurse and 'get' human lab values, PH, etc..but this water stuff?? AACK!

[PoolDoc]

We call them 'guess-strips', for a reason. (Actually, my experience with pool test strips has made me nervous about the fact that similar strips are used medically. It makes me wonder how often they are validated!)

You need some CYA. If you have access to a Sams Club, check and see if they sell "PoolBrand" dichlor shock in a 24 x 1lb box. Most do; and at a very good price. The bagged shock in that brand is undiluted and unblended (good!) -- each bag will add about 4 ppm of chlorine to your pool, but also about 3 ppm of CYA. By the time you've used 2/3 of the box to chlorinate, you'll also have a good CYA residual.

If you can't get it at Sams, you'll probably need to order online. Walmart, Costco, Kmart and most pool stores are selling a blended mess of dichlor and other goop. Lowes and HomeDepot vary by location, but you'd have to be an expert label reader to get the right stuff IF they have it. This product from Amazon is also unblended dichlor:

Kem-Tek Dichlor 22 lbs (http://www.amazon.com/exec/obidos/ASIN/B0030BEHZA/poolbooks)

[tokmom]

Thanks pool doc. My mom has a membership to Sams, and it's an hour away, so that might be the way.
We do have a bottle of HTH stabilizer HTH at 96%. I'm assuming the other 4% is the goop you are talking about and this other stuff is more pure shock, correct?

We will look into Sams or order online on Amazon. Thanks for the link. That helps a lot.

Oh, as for the test strips at a hospital. Most are used for baseline and anything untoward is sent to the lab. At most hospitals I have worked at anyway. :)

[PoolDoc]

Stabilizer that is 96% cyanuric acid is fine to use; normal production cyanuric has, I think, up to 5% impurities and inerts present.

[tokmom]

Good to know. Thank you!

[tokmom]

UPATE: After our shocking the pool and adding CYA, we saw our CYA actually go up to 45. That was 2 1/2 lbs to the skimmer. That 2 days ago.

We tested today (pool still covered with solar cover with rainy cool weather) and the numbers are as follows:

FC 10 with the smaller volume test or 8.8 with larger. (why the difference?)Did my husband mess up?
CC 2
TA 80
CY 45 ish..
PH 7.2

(we need to get a refill for the Taylor CYA test)

Why did the CC go so high after shocking and adding stabilizer? Is this normal? The weather will be nice this Sunday, so we are hoping to swim. Husband says the pool does have a stronger chlorine smell this morning.

thanks.

[PoolDoc]

Why did the CC go so high after shocking and adding stabilizer? Is this normal? The weather will be nice this Sunday, so we are hoping to swim. Husband says the pool does have a stronger chlorine smell this morning.

When you cover a pool, CC's and CC precursors -- pool goo -- can't escape. Pool goo (it's a technical term here ;) ) consists of bad pool chemicals, sweat, pee, suntan lotion PLUS whatever else gets in the pool and reacts with chlorine. Sunlight, chlorine, and aeration get rid of pool goo. Lose the sunlight, and cover the pool with a vapor-tight cover, and Voila', you have an indoor-chemistry pool. Indoor-chemistry pools have problems with goo.

So, while I don't know exactly where YOUR particular CC's are coming from, they aren't unexpected.

Does that help?

[tokmom]

Ok, I wondered if the pool being covered for a good couple of weeks had anything to do with it. The sun (GASP!) has decided to make an appearance today. Maybe we will take off the cover and let it air out.
Should we see if the CC drifts down on it's own in the next few days?

I like the word Goo. At least I understand it, lol.

[PoolDoc]

Ok, I wondered if the pool being covered for a good couple of weeks had anything to do with it.
Very likely.


Maybe we will take off the cover and let it air out. Should we see if the CC drifts down on it's own in the next few days?
Yes, please.



I like the word Goo. At least I understand it, lol.

Thanks, I prefer the sort of naming that nuclear physicists do (it's a "quark") to the sort the military and school teachers do (CRT = "Criterion Referenced Test" . . . ????) or physicians ("Doc, my skin is red and inflamed!". "Yes, you're suffering from erythema." "Wow, thanks, Doc! I never would have known." [ erythema = red & inflamed skin ])

But, I slip sometimes. Currently, I'm using the phrase "epistemologically modest" a lot (not here, in my other life), and currently only my sons know what I mean, sorta, kinda. Unfortunately, every other way I've tried to say it takes a paragraph or more.

[BigDave]

"epistomologically modest"? Is this intended to be an insult (doesn't sound like you)? Akin to calling someone obtuse? Or do you mean the understanding and incorporation of the knowledge that one's knowledge, no matter how developed, is woefully incomplete. Leaving behind the pride one may have of his own knowldege and adopting a more humble view of one's self?

[PoolDoc]

"epistemologically modest"? Or do you mean the understanding and incorporation of the knowledge that one's knowledge, no matter how developed, is woefully incomplete.

Yes, that. It hadn't occurred to me that it could be an insult, but I see that. But, I wouldn't use the word "woefully". Rather I would say the knowledge possible to us is sufficient, but the areas of certain knowledge are far less extensive, and far more pragmatically rooted, than any classical Western thinker would have admitted. And, I would say that the "woe" we feel is rooted not in need, but in arrogance.

It's a concept I've been working with, as I've tried think about what sort of knowledge is actually possible, if one recognizes the problems that led to "epistemological despair" (post-modernism), and acknowledges the "epistemological hubris" of the past, in both modernist and theological rationalism. Ironically, some of this was fleshed out, in my mind, over the past 2 years, as my younger son and I have worked with a group of teen Burundian boys, via Scouts and church. The struggle to communicate with them effectively, given their limited English and my absent Kirundi and Swahili. More than that, their conceptual poverty -- an idea I never encountered before I met it in individuals -- has reshaped, in very substantial ways, the manner in which I think about communication, and understand literature from the past.

The concept is related to CS Lewis' Mere Christianity, in both derivation and content, though what CS Lewis himself said about such things was usually only implicit.

Still, this is massively OT. I will probably be opening, after the 4th, a access-by-request-only section of the forum in which such things will not be OT.