What chlorine level to shock -- now that half my CYA is gone

[JimK]

I added five 121 oz jugs of 8.5% bleach around 7:30pm (it's been raining today so no sun) and brushed the entire pool. I just checked CL level (9pm) and it barely registered! This is what it measured:

FC < .5
CC < .5

Strange......... The water is cold (about 60); does this impact the DPD Powder test?

Does this mean I'm fighting ammonia? Should I go ahead and add the other 5 jugs tonight, or wait until morning?

PS -Just found this in a Google search:

"...11. When a DPD chlorine test flashes a little pink then turns crystal clear, your water has almost no chlorine in it.
The opposite is true! More spas are fried and bathing suits bleached because of this error than just about any other. As you know, the universally accepted DPD test for chlorine turns progressively more pink as higher residuals are encountered in the sample… that is until the indicator is itself reverts to a clear resultant. This phenomenon occurs somewhere near 20 ppm chlorine, the actual value varying with different pH or total alkalinity conditions. Many, many untrained operators or “helpers” have dumped excessive amounts of chlorine in their water (most often in hot whirlpools or spas), thinking all along that for some crazy reason they just hadn’t yet put enough in to get a reading! In a small body of water this testing error has resulted in a few hundred parts per million chlorine residual, creating some very unsafe, damaging or at least unpleasant conditions..."

I didn't notice it "flash pink", but I'm wondering if the CL level is over 20 causing a reading error? Out of curiosity, I did another sample and added several scoops of powder (maybe 4 to a 10mil sample?) but that didn't seem to change anything.

Thoughts?

PPS - Found on Taylor site where FAS DPD test can measure up to 20ppm. Hmmmm.... I have a hard time imagining all that chlorine was gobbled up in 1.5 hrs....I'm thinking CL may be higher than 20ppm so I'm not getting a good reading. I'll hold off adding more CL tonight and check it again in the morning.

[PoolDoc]

The 'pink then clear' transition occurs with the DPD tablets; not the with the DPD FAS test.

But . . . while cleaning this up, it might be better to use an OTO drops kit -- OTO is not too accurate, but it's bomb-proof, in the sense of no false-positives OR false-negatives.

OK. Do this:

1. Use borax to push your pH to 7.8 or so.
2. Tomorrow PM late, add (10) gallons of plain bleach.
3. Test with OTO & phenol red in the AM. Add borax as needed to maintain the 7.6+ pH. Remember that phenol red will not return accurate results if the chlorine is very high.
4. Repeat this cycle till you can sustain a strong chlorine reading overnight.
5. At that point, you should resume using the K2006 testing.

It may take a LOT of chlorine to recover. Unfortunately, with a vinyl pool, draining and refilling is not really an option. If you'd like, you can probably drain to 1 foot above the highest horizontal surface, and then refill. (Ie. you can't drain a pool with vinyl covered steps!).

However those are your options, so you just have to suck it up, vow to NOT let 'slime' (CYA-eating bacterial and algal biofilms) grow next winter, and dose with chlorine till you're done, no matter how much it takes.

It's possible to figure out approximately how much total chlorine you'll need. But other then scratching a mental itch, that information has no value: you do NOT want to do an all-at-once dose; there's too much chance you'd bleach your liner.

So, dose, check, adjust pH, repeat . . . till it's all done.

Here's hoping it won't take much.

[BigDave]

I hate to sound like I'm contradicting PoolDoc, but, I do see a value (beyond my itchy brain-scalp-very itchy) to figuring how much chlorine will be needed and that's how much to buy. The logistics of buying, moving, and storing enough chlorine for an algae / ammonia clan-up may be well worth considering; especially for us weekend warriors who can only collect the materials on Saturdays.
My two cents

[JimK]

I hate to sound like I'm contradicting PoolDoc, but, I do see a value (beyond my itchy brain-scalp-very itchy) to figuring how much chlorine will be needed and that's how much to buy. The logistics of buying, moving, and storing enough chlorine for an algae / ammonia clan-up may be well worth considering; especially for us weekend warriors who can only collect the materials on Saturdays.
My two cents

Thanks Dave.

I'm also limited to when I can buy supplies and try to have everything on hand in advance (I figure what I need based in last seasons).

[JimK]

Thanks Ben.

Looks like I've got a few more items to pick up.

The info I found on the Taylor site referred to the FAS-DPD test using the powder and mention a max test limit of 20ppm:

https://www.taylortechnologies.com/C...P?ContentID=11

.The latest trend among service professionals and a significant number of health officials is testing chlorine with FAS-DPD. This variation of the traditional DPD method allows users to measure both free and combined chlorine levels as low as 0.2 ppm—the maximum allowable level for combined chlorine according to most health authorities as well as the Association of Pool & Spa Professionals (ANSI/APSP)—and as high as 20 ppm. By contrast, the color comparators used with the standard DPD test generally allow readings at the low end of 0.5 and 1 ppm and at the high end of 5 or maybe 10 ppm.

(Bold added)

I'll test again tomorrow morning and see what I get.

Btw, I understand high CL will give false pH readings, so how do I accurately measure pH while shocking? Also you said, vow not to let CYA eating slime grow next winter.... How do I prevent it? Seems like whether or not I lose CYA over the winter has been a crapshoot in the past.....most years no/little loss, a couple times big loss. I don't know what I may or may not be doing that causes this.

Btw, I took a look at what I did at opening last year (I keep records of my pool maintenance) and I added the same amount of bleach, but I didn't test CL until the next day (I got a reading of 16.5). I'm hoping the issue this time is I'm not getting a good reading because CL is over the FAS-DPD test limit, and not that there is so much ammonia that I'm just pouring bleach into a black hole! I should have an answer for this tomorrow.

Oh....forgot to ask.....is it ok to leave CYA at 30 until CL holds? Is this high enough to prevent sunshine from completely depleting CYA?

[PoolDoc]

Losing CYA is a bio-degrative process: no "bio"; no CYA loss.

Covering a pool stops solar loss of chlorine, and it mostly stops algae, but it does not stop bacteria, especially once the chlorine is gone. Maintaining minimal chlorine levels under the cover, will almost certainly stop the process. BUT, one class of the operative organisms is Pseudomonas genus, a group notorious for forming sanitizer resistant biofilms.

Following this process of winterization should do the trick:

1. Stop using the pool at least 1 week before closing (to allow all human added organics, etc to be oxidized and/or filtered).
2. Physically clean the pool at this time, removing all leaves and debris, and brushing thoroughly to break up any forming biofilms.
3. Run the filter 24/7 during the final week. (Same reason). Clean the filter 1/2 of the way through the week, to remove all goop from the filter.
4. Raise the pool to maximum chlorine levels at the beginning of this period. Allow it to drop to high-normal levels by week's end.

5a. Winterize the pool OR
5b. Cover the pool, but do not winterize that that time.

6a. Check weekly while water temps are > 60 degrees to maintain chlorine levels OR
6b. As above, but circulate the water for several hours (or for 1 hour per day every day)

7a. --
7b. Winterize the system, once freezing temps are imminent, or water temp is below 50.

8. Continue to maintain chlorine levels all winter, with monthly checking.

9a. Once water temps rise above 60 degrees, check chlorine weekly.
9b. As above, but also open the circulation system, while leaving the pool covered.

10. Open the pool.

[PoolDoc]

Dave has a point about accumulating chlorine.

If it's not convenient to purchase bleach every other day or so, it may be worthwhile to do a chlorine demand test: http://pool9.net/bucket-demand

[JimK]

I need to print out that post about closing for future reference.

I'll check out that link also.

Thanks.

I'll report again tomorrow.

[JimK]

Day 2...

Hi Ben. I got the items you suggested (borax, OTO/Phenol Red test kit, 8.5% bleach - I have 19 jugs on hand now (121oz each).

I used the OTO kit to check CL and pH to see how it matched up with the Taylor kit.

FC - 0
pH - 7.2 (before adding borax; I'll test again in about an hour)

So it matches the Taylor kit results.

This evening I'll add the bleach as you recommended.

Is it OK to let the pool go all day with 0 CL???

[JimK]

.....
OK. Do this:

1. Use borax to push your pH to 7.8 or so.
2. Tomorrow PM late, add (10) gallons of plain bleach.
3. Test with OTO & phenol red in the AM. Add borax as needed to maintain the 7.6+ pH. Remember that phenol red will not return accurate results if the chlorine is very high.
4. Repeat this cycle till you can sustain a strong chlorine reading overnight.
5. At that point, you should resume using the K2006 testing.

....

Ok...here we go...did my homework for today.

Added borax this morning to raise pH
Per post above, added some bleach to carry it through the day since this morning's test showed 0 CL
Added 10 jugs of bleach about 8:30pm.

I'll give it about 1/2hr to mix then test to see if any CL shows up this time. I'll get up early tomorrow and test again.

Here's hoping.......

EDIT: Just checked CL using the OTO kit; sample turned dark orange....a good sign! We'll see what it looks like in the morning. Keep your fingers crossed.......