Chlorine Demand - Par Pool & Spa has a good handle on how to treat this growing issue.  If you haven't dealt with it yet, you will

Question:
I've been having the "disappearing chlorine" problem and I am trying to achieve breakpoint chlorination. 

I have an 8500 gallon pool and I added appx 2 lbs of non-chlorine based shock, then 6 lbs of chlorine based shock - that was Tuesday night (and added two tablets in the chlorinator). 

48 hours later I used one of those new test kits that tests for both free and combined chlorine and here's what I got: 

1st try - 20ppm FAC, 1.5ppm combined

2nd try (20 minutes later) 17.5ppm FAC, 1.0 combined

Do you think I have achieved it?  If not, what else do I need to do?

Response:
If you're holding onto 17 ppm FAC, the 1.0ppm CC shouldn't make a big difference.  Retest after 2 days to verify that the chlorine is still holding.  It should be least 10.0 ppm FAC.  If it drops down to 3.0 or less, I would recommend shocking with another 10 to 12 lbs. of shock.

Also, what is the pH?  If the pH is low (under 6.8 especially), you will burn through chlorine quickly.

Follow Up Question:
Thanks for the advice - I just tested again this morning, 4 days later, and I think I might have "jumped the grand canyon"... 

I've got 9.5 FAC and 0.5 CC, my PH is around 7.2, maybe a tad higher (hard to tell for sure with the color coding).  Do you agree that I have achieved breakpoint chlorination?

If so, is it safe to swim with chlorine at these levels?  How about using the attached hot tub?  I'm thinking it might be too high for the hot tub, but maybe not the pool?  What would you say is the safe limit of FAC to swim? (My 3 year old is getting a little antsy)

Thanks again for the advice.  By the way, I read a lot of different articles about chlorine demand and breakpoint chlorination in my search to fix the problem, and I must say that your website was the most informative, and easiest to understand.

Follow up response:

Congratulations!!  It all sounds good.  The chlorine is a little high.  Typically we want to wait for the chlorine level to drop to under 3.0 ppm, but...many water parks & commercial pools often have chlorine levels as high or higher.  If your daughter has sensitive skin, you may want to keep her out.  But a few minutes in the pool with a good shower afterward should be fine.

In the hot tub, you're going to get a good "gas off" of chlorine between the warmer water & the jet action.  It should come down relatively quickly.

You can also turn down or off your automatic chlorinator or remove the chlorine tabs or sticks from the skimmer for a day or two also.  Put them back in when the chlorine level has gone to under 3.0 ppm.

We have a new pool care website launched (www.pool-care.net).  Its sister site is more functional (www.spa-care.info).  They're both dedicated to pool & spa care info only, most is going to enhance the content that you've already seen.  We'll include your question in the "We've been asked..." section.
 

Question:
Can a non-chlorine shock help to oxidize the contaminants rather than adding the high volume of chlorine shock necessary to reach the break point in a pool with a chlorine demand issue?

Response:
A non chlorine shock or oxidizer like BioGuard Oxysheen will break up some to most of the chloramines that are adding to the chlorine demand, but will normally not get you to breakpoint.  In REALLY high chloramine situations, we normally use Oxysheen to bring those chloramines down first (usually at a rate of 2 lbs per 10,000 gallons which is a little overkill).  When using ANY kind of shock treatment, be sure to remove the solar blanket or automatic cover so that all of the oxidized junk can "gas off" into the air.  After a couple of days, we'll do a second Chlorine Demand test & reevaluate the Chlorine Demand.

I know that's a "sort of" answer, unfortunately, there are too many variables when it comes to chlorine demand & chloramines are just a part of that equation.
 

Question:
Looking for info & think I found the right place-use the same brand of chemicals as advertised on your site-Having a rough start with the pool this year & finding the store personnel not as knowledgeable as I would hope-Our pool had 2 dead squirrels plus tons of algae-ugh...have it pretty clean by now by alternating clean filter cartridges, along with algaecide & Smart Shock- Finally brought the water in to be tested-showing zero level of chlorine-computer testing called for 17 bags of Burn Out-

Of course that sounded ridiculous (little did I know) and since the print outs in the past usually recommend overkill on some of the products- I bought a case of 12 bags- I was concerned about what it would do to the pool liner -Store employees did not explain well enough, said I could try 6 bags one day, then 6 the next.... Any way-I now realize that I will need more shock at one time to break the combined chlorine-but am still quite apprehensive about that many bags dissolving without damage to the liner-Even after stirring the foam from the 6 bags & brushing some did not appear dissolved- Can you recommend an equivalent amount of liquid chlorine for a pool with approx. 13,000 + gallons of water-realize I will then probably have to add Lo & Slo to adjust the pH...Or should I just go for it & try the 17 bags at once?

Response:
I would fear that the 17 bags will be insufficient.  Get another sample to them & make them do a chlorine demand test.  If they don't have the new AccuDemand 30 station, tell them to invest the $500.00 + in it!

Alex & the normal BioGuard test station will only take into consideration breakpoint chlorination and not chlorine demand.  Our own in-store tests show a BIG difference between the 2 tests -- normally calling for 2 to 3 times (so in your case 30 to 50 lbs. Burn Out) the amount to satisfy the demand!!  I'm not kidding!  The good news is it works!  Our customers report back dramatic changes, relatively quickly.

As to liquid chlorine, that will be your biggest waste of money that you could do.  Liquid has only about 12% available chlorine (when it's initially packaged) as compared to about 60% with Burn Out.

That's the good, bad & ugly.  But, it's the way things go.  Understanding chlorine demand is of growing importance. 

Follow Up Question:
Thank you for your prompt response-I plan to call my local store (NY) to check on the chlorine demand testing-In an effort to do anything other than buy & add up to 50 lbs. of any product I did call another store who recommended using 3 bags of non-chlorine shock-potassium monopersulfate to break the chlorine lock-Does BioGuard have a product like that?

Thought I'd give that approach a try-How can you tell if the lack of chlorine reading is due to a lock or demand? Might be less expensive to drain a third of the pool and refill???  

Follow Up Response:
3 bags of monopersulfate (BioGuard Oxysheen) are not going to do anything.  8 to 10 will have some effect.  When you're trying to take care of a chlorine demand / chloramine problem, you can't play with it.  Trying to save money is only going to cost you more, very soon.  Not to mention a continuing problem all season long. That's why the chlorine demand test is so important.

A partial drain & fill will help, BUT then you have all of that rebalancing of the water to do.  AND it's not going to rectify the problem.  The problem will continue to worsen as the summer goes on & you want to use the pool.

Our local chlorine demand testing is showing superb results.  Customers aren't necessarily happy with the cost, but their problems are done & over with.
 

Question:
I am having a chlorine problem with my 19,000 inground vinyl liner pool.  My combined chlorine is 10 and my free chlorine is 0.  My PH is 7.7 with Total Alkalinity 128.  My pool dealer says to add 35 bags of shock.  I understand I need to achieve breakpoint chlorination (your website has some good info, by the way).  Is there a more economical way to do this? 
What if I wait a few days- will the Combined Chlorine do down?  And if I do super chlorinate, do you recommend regular chlorine shock or the chlorine free?  How long do you think it will be until the chlorine levels return to a normal and safe swimming level?

Response:
If you were my local customer, I would first have you use 10 - 12 lbs. of a non-chlorine shock to help bring down the combined chlorine.  I would be afraid that the 35 lbs might not be enough & would make the situation worse.  Hopefully your dealer has a chlorine demand station to give you an accurate test (look for a BioGuard dealer with the new Accu- Demand 30 test station, it's 99.99% accurate).  After adding the non-chlorine shock, such as BioGuard Oxysheen, retest it after 24 hours.  When it's under 4.0, then do a chlorine shock.

Unfortunately, there's no easy way to deal with this situation.  The combined chlorine will not go away; if anything it will worsen. You're on the right track!