need final word on shocking/re-entering pool

[powiebaby]

Hi, all.

I've done much web-browsing on this and can't seem to find a satisfactory answer. First, my specs/usage/testing/maintenance stats:

I have a 15x30 10,600 gallon AG pool. Live in Boston. I would say the usage is relatively light on a weekly basis. Usually only 2 kids in the pool for a couple hours a few days a week. My pH has been good.....around 7.5. Cl usually within 1-3. The water is very clear. I spot scrub/vac the bottom edges and walls a couple times a week if signs of algae begin to form (light brown spots), and I vacuum the pool about once a week. A month ago, I had the water tested to see how my own testing results were matching up. Ph and alkalinity were on target. Added some stabilizer as directed. My maintenance routine for the Cl is I add small amounts (4-6-8 oz) of the 12% liquid shock every couple of days as the Cl reading nears 1.0 or lower. And in addition, I constantly maintain 7-8 of the tiny 1" Cl tabs to the floater and add more as they dissolve.

When I add my 4-6-8 oz of liquid shock, the Cl reading later on is usually around 4 or above (test kit only goes to 4 - will probably take the advice and get a much better test kit). Couple times so far this year when I shocked with 1 lb Cal-hypo packet, the Cl reading would go what I suspect is way above 4, probably upwards of 6-10. And that would take 2-3 days or so to come down on its own to a respectable 4 or the ideal 1-3 range.

So my question is 2-part. Is it really safe to go swimming in the pool if the Cl reading is 4 or higher? I even bought the Dichlor shock packet that says you can swim in as little as 15 minutes, but the small print says as long as the Cl is within acceptable range. Even if my Cl reading is below 1.0, an hour after adding the Dichlor shock the Cl reading is 4 or higher. Let's skip the BBB method for now and concentrate on the chemicals that I have on hand. Please critique my pool maintenance so far and give me recommendations going forward. What, if required, should I be doing for shocking the pool during the evening such that I can swim the next day?? Is my current routine satisfactory, even if inefficient? I've read that if you use Cal-hypo during the evening, then you can swim 8 hours later (next day) without concern. But the Cl reading is definitely going to be over 4 the next day. Is it generally safe to swim if Cl is somewhere between 4-10? I've read here and there that it is okay. Not concerned about bathing suits, just general health of sending kids in the pool. Obviously, I want a sanitized pool that is safe (Cl reading) to swim in.

Thanks for your patience and responses.....

[aylad]

Hi, all.

....ideal 1-3 range.

So my question is 2-part. Is it really safe to go swimming in the pool if the Cl reading is 4 or higher? I even bought the Dichlor shock packet that says you can swim in as little as 15 minutes, but the small print says as long as the Cl is within acceptable range. Even if my Cl reading is below 1.0, an hour after adding the Dichlor shock the Cl reading is 4 or higher. Let's skip the BBB method for now and concentrate on the chemicals that I have on hand. Please critique my pool maintenance so far and give me recommendations going forward. What, if required, should I be doing for shocking the pool during the evening such that I can swim the next day?? Is my current routine satisfactory, even if inefficient? I've read that if you use Cal-hypo during the evening, then you can swim 8 hours later (next day) without concern. But the Cl reading is definitely going to be over 4 the next day. Is it generally safe to swim if Cl is somewhere between 4-10? I've read here and there that it is okay. Not concerned about bathing suits, just general health of sending kids in the pool. Obviously, I want a sanitized pool that is safe (Cl reading) to swim in.

What is your CYA level? The answer to that question will give us the answer to all your other questions. The chlorine level that you need to keep in the pool to keep algae away and to keep it sanitized, as well as the chlorine level you need in order to reach "shock" level, all depend on your CYA. And if you've been using trichlor pucks and dichlor, I'm guessing it's pretty high--in which case you will need to keep your chlorine higher than 1-3.

Janet

[AnnaK]

Is it generally safe to swim if Cl is somewhere between 4-10?

My FC goal is 4 ppm and my water normally tests betwen 3 - 5 ppm. I swim daily as do my dogs. I use a combination of trichlor and 12% bleach. The trichlor is added during the night when the pump runs and I add the bleach in the mornings after water testing if I need to raise the FC. When I add liquid bleach I 'stir' it in by swishing the water around with the skimmer net on the pole. We generally swim within 2 hours of adding the bleach.

I've kept the FC as high as 6 ppm when my CYA value was higher and there were no negative effects swimming in the water.

Anna

[powiebaby]

OK, I essentially got the answers I was looking for from a guy at our local mom and pop pool store. He told me a couple of things. 1. when you shock, initially the Cl goes up, but as it interacts with the water and the nasties within, it comes down to acceptable levels after a short period of time. The regular shock that you put in during the evening and run the filter overnight, the pool should be okay for swimming in the next day. The quick shock that you can swim in after 15 mins or so, it's just that. And for comparative measure, he told me that your typical large public pool, like a YMCA pool or hotel pool, has a much greater level of Cl to account for the large number of bathers. He told me it's typically around 7-10ppm, if not more. And we've had our kids in those pools often. So I think that I should be okay with sending the kids into the pool even when the Cl reading beyond 4.0 on the test kit, provided I follow the directions on the particular type of shock that I use. I'll still aim for the ideal reading between 1-3, but won't fret if the Cl registers 4.0 or above at 10am on a hot, sunny Saturday.

[KurtV]

... I'll still aim for the ideal reading between 1-3, but won't fret if the Cl registers 4.0 or above at 10am on a hot, sunny Saturday.

As others have posted, knowing the free chlorine level without knowing the CYA level is essentially useless. CYA has a great deal of bearing on how the chlorine will effect bathers, liners, swimsuits, etc. In your case, unless you have very little CYA (like less than 20 ppm), 1-3 ppm is far from ideal. In fact, it could be dangerous as you will have insufficient chlorine to keep your water free from algae let alone sanitary.

Post your CYA level and people here will be more than happy to give you advice that will serve you well.

[chem geek]

The "quick shock" your pool store guy is referring to isn't chlorine, it's non-chlorine shock (potassium monopersulfate) and they recommend waiting 30 minutes before going in the pool after use (it used to be 15 minutes, but they changed that). Anyway, as for chlorine, with an outdoor pool with Cyanuric Acid (CYA) in it, the disinfecting chlorine level that actually does the oxidation of organics, killing of bacteria and algae, etc. is very very low. A pool with 10 ppm Free Chlorine (FC) and 30 ppm CYA has the equivalent disinfecting chlorine level of 0.45 ppm FC with no CYA so is less than found in most indoor pools.

He is wrong about chlorine dropping quickly after shocking. It all depends on whether there is a lot of algae or other substances for chlorine to combine with and you can test the chlorine drop yourself to see. It is true, however, that chlorine will drop quite a bit during the day in direct sunlight, but that happens whether you have something for chlorine to combine with or not.

At any rate, yes, it is safe to swim after a modest shock, but if there are organics to oxidize, then they may smell briefly until sunlight breaks them down so I'd wait a half hour or so right after shocking before going in.

Richard

[AquaBill]

Richard:
How is it that "a pool with 10 ppm Free Chlorine (FC) and 30 ppm CYA has the equivalent disinfecting chlorine level of 0.45 ppm FC with no CYA"? Is there a typo in that? That is a ratio of over 20 times. Looking at Ben's "best guess" chart below I would have thought that 10 ppm FC at 30 CYA would have been equivalent to somewhere around 5 ppm FC at no CYA.

Stabilizer . . . . . . Min. FC . . . . Max FC . . . 'Shock' FC
=> 0 ppm . . . . . . . 1 ppm . . . . . 3 ppm . . . . 10 ppm
=> 10 - 20 ppm . . . . 2 ppm . . . . . 5 ppm . . . . 12 ppm
=> 30 - 50 ppm . . . . 3 ppm . . . . . 6 ppm . . . . 15 ppm

..Bill