Chlorine is GONE

[clueless at times]

Hello all. I live in south Texas. I have an in ground 9000 gallon plaster pool. The pool was re-surfaced three years ago so the water is not too old. It has a Hayward cartridge filter with an in line chlorinator. I have had this house and pool for five years and NEVER had a water problem. This was a very heavy spring for oak and there are several oak trees surrounding the pool. It was a leaf trap this spring but other than that there have been no problems. About a week and a half ago I started to notice some light greenish algea on the sides and steps. It would brush away easy enough but comes back the next day. Not heavy, just a light coating . Shock would normally end this problem. I began to shock the pool with little to no results. I have a Taylor test kit and tested the water often. I would normally see a drastic chlorine raise after shocking but this time the test results still showed a very low chlorine content. I continued to shock, brush, clean the filter and fight this problem. I can’t get the chlorine level to rise up to levels high enough to kill off the algea. Four days ago, fearing a CYA problem, I took a water sample to Leslie's Pools to have it tested. Here are the test results:

CYA: 40
FAC: O
TC:0
TA: 110
PH: 7.6

Total dissolved solids were 250
and phosphates were 0

I was told my chlorine was probably unstable and given three one pound bags of "Free and Clear" which is an oxidizer according to the package. I was told to treat the pool with the oxidizer which should free up the chlorine. Last night I still had slight algea and tested the water and found it had a very low (1.2) chlorine level. I know chlorine is needed to kill the algea. I have continued to treat the pool with about two pounds of shock and a gallon of bleach each time I shock over the past several days and can’t get the chlorine level up to normal shock levels. At this rate I am afraid that I might need to drain it but am afraid of what the real problem is. The filter is green each time it is washed out from trapping the algea after brushing so that is working. Returns are all flowing at what feels like the normal rate and pump pressure is normal. I am at a loss to figure this out. Any advice?

[Watermom]

In a 9000 gallon pool, each quart of 6% bleach will raise the chlorine by 2 ppm. 4 quarts per gallon, so a gallon will raise it by 8ppm. (Remember, most jugs of bleach sold these days are not gallons, but only 3 qt. jugs.) What kind of shock are you using, by the way? (ingredients)

With a cya of 40, your shock level for your pool is around 15. So, instead of using "shock" and bleach, why don't you just throw 2 gallons of bleach in there. That should take you up to shock level. Remember, the key to killing algae is to sustain the shock level and not let it yo-yo up and down. Test at least twice per day ( and 3x is even better) and each time, add enough bleach to take it back up to shock level. Also, run the pump 24/7 while you are clearing the pool. If you do this consistently, it will work.

And, welcome to the forum!

[clueless at times]

Thanks for the welcome. I am not sure of the exact contents of the shock, its "Chlor-Brite" sold at Leslie's Pools. I have dumped so much of this along with bleach into this pool the last few days that it is almost impossible for me to believe it would take more. I have poured at least six of the large bleach bottles and twn pounds of shock over the last five days but I will continue on. I have been running the pump 24/7 for several weeks and although the water is pretty clear, the algea continues to grow. I was wondering if there was a reason that it wont hold its chlorine level that would make sense to me. I guess I am so used to seeing instant results from shocking that when little happens it causes me to think there may be another problem. Thanks for the response to my post!

[Watermom]

How many times a day are you testing and how often adding bleach and/or shock?

[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.