Super high combined chlorine

[themaccs]

Help!! Started having problems the end of last season with chlorine disappearing - at that time I had a CYA over 100. I don't remember having problems with high CC levels - just chlorine disappearing like crazy. Fast Forward to trying to get things going this season. My CYA dropped to between 30 and 40 and I can't seem to get rid of my really high combined chlorine levels. Earlier this week I had pretty good readings at the pool store (didn't have refills on some of my home testing agents yet) - FC - 2.5, CC - 0, pH 7.4, TA - 180, CH - 210, CYA - 40. Pool is 19,500 gallons. I made the mistake of not testing for a couple of days and yesterday when I tested CC was out the roof again. I added about 10 gallons of bleach (6%) last night. This morning readings are as follows:
19,500 gal vinyl liner pool with cartridge filter
FC - 0.2
CC - 5.5
pH - 7.2
TA - 160
CH - 210
CYA - <30 (but looks like it is pretty close to 30, certainly above 20)

Water looks almost perfect - a little foam when I first open the electric cover in the morning that goes away as soon as the cover is open, but otherwise pretty much clear.

My plan for the day - add 17 gallons?? (do I really need this much? - I am really concerned about damaging liner) bleach this morning and brush, check again at noon and add chlorine as needed, check again this evening and add chlorine as needed - and keep doing that all weekend. I may use a little stabilized chlorine to get my CYA up just a bit. Am I on the right track? How do I handle my pH with my TA high?

Thanks for any help you can offer me!

[aylad]

First of all, welcome to the forum!! We're glad to have you here....

So, to help with your questions...
First of all, I would leave your TA alone. In a vinyl pool, 160 is okay. Depending on your fill water, it may lower some over the summer due to splashout and refilling, or if your pH gets too high and you have to lower it, you can deal with the TA at the same time. For now I would leave it alone, it's fine.

I'm a little confused about your high CC reading--are you sure you don't have the CC and FC backwards? A pool with 5.5 CC and only .2 FC ordinarily wouldn't be clear. What testing method are you using? Total Chlorine = Free chlorine + combined chlorine.
Either way...to reduce CC, you can do two things: 1) leave the pool uncovered during the day, and let the sun help remove the CC, and 2) shock the pool. With a CYA of 30, you need to get your chlorine up to 15 and hold it there until the CC is gone. In your pool, each 1 1/2 quart of 6% bleach will raise your FC by 1 ppm, to go from .2 FC to 15, you would want to add 5 gallons of bleach. Test for FC and add whatever amount of bleach you need to bump it back up to 15, and the more often you can do this the faster the CC will clear. Once the CC is less than 1 ppm (hopefully 0) you can let the Cl drift back down.

Do not add 17 gallons of bleach at a time--you will kill your liner!!

Janet

[chem geek]

It sounds to me like the pool was "let go" (i.e. not chlorinated) over the winter and that bacteria have converted some of the CYA into ammonia. That would lead to a huge chlorine demand upon opening and initially any chlorine added to the pool would form monochloramine which registers as Combined Chlorine (CC). I describe this technically in this post and describe my own experience with this in this thread.

The bad news is that if the bacteria truly converted around 60 ppm CYA into ammonia, it would take at least 150 ppm FC cumulatively added to get rid of. Hopefully, some of the ammonia outgassed so that the actual amount needed won't be that high, but it will take a lot regardless. So keep adding chlorine with the pump running adding it over a return flow in the deep end and measure the chlorine level after 30 minutes. If the FC is still low, add more chlorine. The CC may continue to climb, but keep adding chlorine until the FC starts to rise. At some point you'll reach breakpoint and the CC will start to drop.

Do not add any stabilized chlorine at this point. A higher CYA level will only make the process of getting rid of CC take longer. Do not worry about the pH and TA at this point either. Having the lower pH to start with is fine since shock levels will tend to raise the pH anyway (at least temporarily when the FC gets high)

To prevent this problem in the future, maintain chlorine in the pool over the winter. If you live in an area where the pool freezes over, then shock the pool with chlorine when it gets below 50ºF and then open the pool up again before the temps get above 50ºF. Chlorine usage is very low at colder water temps.

Richard

[themaccs]

Thanks for your reply - No, I do not have the numbers backwards- My guess is that I have the situation Chem Geek describes in his response and the only thing I know to do is to keep adding chlorine. So I guess I'll keep adding and checking, adding and checking and pray my liner survives.

[themaccs]

Thanks chem geek - I had pretty much come to the conclusion I must be experiencing what you are describing. With fear and trepidation I went ahead and added the bleach like I described - an hour and a half later I still had basically no FC but the CC was down to about 2.5. So I added some more and will check again in 30 minutes, i sure hope i am not destroying my liner. We did have it closed professionally? at the close of last season - I wonder if they forgot a step?

[themaccs]

Well, I don't think I would have believed this if I hadn't experienced it. I have been adding chlorine following Chem Geeks experience ( Thanks - wouldn't have had the courage to do it otherwise!). Gave it a really large dose yesterday morning and then retested and added bleach every 1-2 hours all day yesterday about 1.5 - 3 gallons at a time. Now, some nearly 35 gallons of bleach later, I am still not there yet. I went ahead and added some stabilized chlorine (I was out of bleach) this morning because my FC was down to 0.8 and my CC was still 1.2 and I was afraid to go off to church for a couple of hours and lose the last of my FC. That did get my FC up to about 15, but it is already back down to 2.5 with CC now at 0.8. Off to get more bleach and I will continue today as yesterday. I'm sure glad its a long weekend and I have time to deal with this! I don't know what the nasty thing is that's in my water - but I sure hope I can finish killing it today!! The amazing thing is the water is crystal clear!

[chem geek]

If you want to know how much more chlorine it will take you can do a bucket test where 1/4 teaspoon of 6% bleach in 2 gallons of pool water is 10 ppm FC. That will tell you how much cumulative FC you have left to go. If one does this initially, then one can decide whether it's better to do a partial drain/refill if water is less expensive than the amount of chlorine required. One can also get an inexpensive ammonia test kit from a pet/fish/aquarium store to get some idea of the ammonia in the water (though that's only part of what needs to get oxidized).

As for adding CYA, just note that it will slow down the rate of the oxidation process. The plus side is that it will retain the FC longer during the day protecting it from breakdown from sunlight, but right now your FC seems to be mostly getting consumed oxidizing the ammonia in the water and that's much faster with no CYA in the water. Normally I recommend not adding CYA until your FC is holding longer. If the FC only drops by 50% in an hour, then that's the time to add CYA since that drop can be from sunlight. If it drops a lot more than that, then it may not be worth having the CYA. If you do add CYA, don't add very much -- even 10 ppm or 20 ppm is plenty at this point, but will slow down the oxidation process by over 10x. Finally, you'll know that sunlight and no CYA are not an issue yet if you add chlorine at night with the sun off the pool and still find the FC getting used up rapidly.

As far as your liner is concerned, just keep the pump running while doing this process and pour slowly over a return flow to ensure thorough mixing and lightly brush the side and bottom of the pool where you add chemicals. Your liner will be fine.

(On a side note, in a conversation with Ben I found out that he first discovered this effect long before I did and wrote about this here and here and in earlier posts. I just independently worked out some of the chemistry involved based on known CYA degradation pathways to come up with some low and high range quantities.)

[themaccs]

Thanks for your help. To say i am frustrated is indeed an understatement. I have already used over 50 gallons of bleach. FC still dropping like crazy overnight and CC which was staying at about .8 during the day yesterday has been staying at about 2.0 since the sun went down yesterday. Decided to drain some water off today, but don't know how much I will be able to accomplish because the pump we use limits us to being able to only drain about 8 inches off, not to mention that i am scared to death of really messing things up with the liner if we drain too much off. So, with the bucket test thing I guess I am trying to create a mini version of my pool? I'm a little concerned about the time that will take in addition to the fact that i don't have an unlimited supply of testing reagents. At this point I guess I am inclined to just put the 8 inches of fresh water back in the pool and continue where I left off with the addition of chlorine. Am I wasting chlorine adding during the day? I thought I understood that it would be best to keep my FC at shock level for as long as it takes to get rid of the CC AND keep my FC from dropping overnight, so my goal at this point has been to keep my FC at between 15 and 20, checking every hour or so and adding whatever it needs to get back to that level. I can do that today - but i have to go back to work tomorrow! Most recent results (before we started draining the 8 inches off:
FC - 16
CC - 2.0
pH - 7.2
TA - 160 ( i have been checking this just once a day)
haven't rechecked CH - seems irrelevant at this point
CYA - 35 - 40 ( i did add some stabilized chlorine yesterday morning since when i woke up FC was down to about 2 and we were out of bleach - didn't want to lose FC while we were at church!)

Again, thanks for the input. Hind site is always 20/20, but in retrospect i should have been more concerned and diligent about figuring out what was going on when the pool started eating chlorine at the end of last season. Didn't have the CC issue then, though, just a bear of a time keeping FC in the pool at all. And a CYA of at least 100 makes me think that some bacteria was introduced at some point so that even though the pool was closed properly last season, the bacteria or whatever had several months of enjoying their CYA meal and "pooping" out ammonia. This is costing me not only with the money I am spending on chlorine and fresh water, but in time and frustration as well. Live and learn!

[themaccs]

P.S. : I thought I might back up a little bit and introduce myself and explain how i got here. I have been lurking in the backround, following advice here (sort of) for about 5 years. We were living in GA then and I found testing the pool myself and managing with a modified BBB (we used a chlorinator and occasionally some stabilized shock) pretty easy- and it beat trying to get a sample to the pool store for testing. It worked pretty well, but then our pool liner ended up getting bleached out and we wondered if it was from using the bleach. That didn't really make sense to me, but at my husband's gentle suggestion, we went back to pool store management of our pool. Then we were transferred here to Kansas in July of 2008 and bought a house with another pool. We continued managing the pool store way, and then for some reason last year I got concerned about that my CYA level might be way high (pool store seemed to ignore CYA) and did a test myself - the results were crazy - I think up around 170! We drained some water out of the pool a couple of times, and I got it down to around 100. I decided to leave it there for the season (now I know a big mistake) and manage with the BBB method and some algicide. This season we took the first couple of samples to the pool store, and while I think the testing methods were accurate and their advice was ok - using lithium chloride to shock at the level and frequency i was needing got really expensive really fast!!! So I started in again testing myself and using bleach. I got frustrated pretty quick because I couldn't keep FC in the pool. My husband's advice was to go back to the pool store and do whatever they suggested to get things fixed. I didn't really want to do that - the expense would have been ridiculous. So, I started searching this site to find an explanation and a plan for fixing the problem. I think i convinced my husband that the advice on here makes some sense and won his support in the process. So here we are, frustrated that this is taking so long and wondering if we will ever get it fixed. But I am fairly convinced that I would be messing with it all summer and swimming in a questionably safe pool if we continued with the pool store advice - not to mention the cost! This way, i am hopeful that once we get this issue fixed correctly, I might be able to enjoy the rest of the summer in an easy to maintain pool. So, thanks to all you experts for being here!

[aylad]

I'm glad you found us and posted here. The ways that we describe here DO work! Sometimes it takes a little longer to get where you want to be, but you have to remember that it took about 2 years for your CYA to build up to the point where it broke down into this much ammonia demand, so an overnight fix is just not possible. And at least bleach is much cheaper than lithium!!

It is easy to get frustrated with it, and to doubt yourself, and to just "give it back" to the pool store--but believe me, you'll have this problem fixed soon and enjoy a whole summer in a clean, clear pool, where if you go with the pool store, this is a battle you're gonna fight all summer long. Patience is hard to come by sometimes, but it's a necessary evil!!

We're glad you're here....

Janet