Chlorine is GONE

[clueless at times]

right now twice a day, this past weekend it was three or four. I am working now so it has to wait until late afternoon. This past weekend I would shock it at least twice a day trying to reach shock levels. My tests never seemed to show much of a raise in chlorine level an hour or even two after shocking. It is like the chlorine level would not change. Of course I heard "locked up" from Leslie's but that makes no sense to me. If I dump enough chlorine (which I thought I did) there should be a change.

[Watermom]

Yes, there should be. Chlorine lock is another one of those things pool stores like to tell you about that are baloney. Keep at it and let us know how it is going.

[chem geek]

Leslie's Chlor-Brite is Dichlor and is the most irresponsible pool product sold as a "shock" (which is really a verb, not a noun) that is on the market. The reason is that with Dichlor, for every 10 ppm Free Chlorine (FC) that it adds, it also increases Cyanuric Acid (CYA) by 9 ppm. If you've added a lot of this to your pool, then you've increased the CYA level as well which makes chlorine less effective so requires even higher FC levels to kill algae.

I would not trust the pool store numbers, especially not for CYA. You really need to get yourself a good test kit: either the Taylor K-2006 you can get at a good online price here or the TF-100 from tftestkits.net here with the latter kit having more volume of reagents so is comparably priced per test. You can compare these two test kits in this post.

If your pool was "let go" over the winter and the chlorine got to zero, then bacteria may have converted some of the CYA into ammonia. So your chlorine demand may be huge. Though any oxidizer could get rid of this, bleach or chlorinating liquid is usually the least expensive way to go -- non-chlorine shock is usually 3 times as expensive.

If you want to get an estimate of how much chlorine it might take, do a bucket test by taking a 2-gallon bucket of pool water and add 6% bleach to it noting that every 1/4 teaspoon of 6% bleach in 2 gallons is 10 ppm FC. Add some bleach, wait an hour, measure the FC. If it's not holding (i.e. much less than 10 ppm FC) then add more, wait an hour, remeasure. Once the FC holds then that cumulative amount of FC is what will be needed for your pool -- it could be a lot.

Richard

[CarlD]

If you want to get an estimate of how much chlorine it might take, do a bucket test by

1) taking a 2-gallon bucket of pool water and
2) add 6% bleach to it noting that every 1/4 teaspoon of 6% bleach in 2 gallons is 10 ppm FC.
3) Add some bleach,
4) wait an hour,
5) measure the FC.

If it's not holding (i.e. much less than 10 ppm FC)

6) then add more,
7) wait an hour,
8) remeasure.
9) Once the FC holds then that cumulative amount of FC is what will be needed for your pool -- it could be a lot.

Richard

Richard, this is a seriously cool test and I think we should consider adding it to our stock of tools.

Thanks!

Notice I broke it up into exact steps to follow.

[chem geek]

That's great. Steps 2 and 3 are the same (i.e. adding some bleach) so step 3 can be removed. Other than that, it's a very clear procedure. Thanks for cleaning it up.

Though it would be nice to be able to predict the amount of chlorine needed solely from an ammonia test and Combined Chlorine (CC) test, it often takes more chlorine than predicted since there may be some partially broken down CYA that doesn't show up either as CYA nor as ammonia and there can also be some dead algea or bacteria that don't show up as CC.

I describe technically how bacteria degrade CYA to ammonia in this post and I describe my personal experience with this effect in this thread.

[clueless at times]

"I would not trust the pool store numbers, especially not for CYA. "

Well that turned out to be accurate. I had the water retested and CYA is 180. I think that explains a lot of my problems.

Thanks to you all for the advice.

[Watermom]

You know how to handle it at this point? If not, give a shout and we'll help. Good luck.