Super high combined chlorine

[themaccs]

Back to being a little frustrated. I seem to be stuck. Still losing between 5-6ppm FC at night. Stuck at about 1ppm CC. pH - 7.2, TA - 150, CYA - 45-50 (i have a little trouble deciding exactly when I can't see that dot!). I have some time at home again today - is it best to try to keep my FC up at shock level as consistently as I can by doing the every hour check thing again today? Or is the cumulative amount of bleach going to be the same no matter what? Yesterday - partly because of working, partly because of wanting to be able to swim in the evening, we let the FC drift down to 8-10 a couple of times, then dosed it back up last night.

And how soon after I dose the pool can I check to get an accurate reading of my shock level? - I have been calculating what I need using the pool calculator, then testing an hour or so later. I am assuming that I reach shock level when I put the calculated amount of bleach in, but since I am still losing some and not checking till an hour or so later, I have never actually had a test read out at shock level. I am considering my shock level at this point to be close to 20 since my CYA is close to 50. The highest test reading I have had as been 16.

Am I missing something?

[Watermom]

I think you just have to keep at it. As soon as chlorine goes in, it starts to get to work. Yes, to your question about trying to keep at shock level as consistently as you can. The more often you test and add bleach back up to shock level, the faster this is going to get finished. You can't test and dose TOO often. I have no doubt how frustrated you are, but keep hammering it with bleach!

[themaccs]

I think you just have to keep at it. As soon as chlorine goes in, it starts to get to work. Yes, to your question about trying to keep at shock level as consistently as you can. The more often you test and add bleach back up to shock level, the faster this is going to get finished. You can't test and dose TOO often. I have no doubt how frustrated you are, but keep hammering it with bleach!

Thanks for your quick reply! Off to buy some more bleach

[AndyJ]

This must be exactly what I experienced this spring. I had heard of CYA-eating bacteria, but didn't realize this would result in more that simply needing to add stabilizer. I had good to high CYA levels last fall (guessing 50-100) and none this spring. Took 102 gallons of bleach before it would hold FC levels.

I'm now looking for ways to prevent this from happening next winter. I'm guessing some combination of chemical levels during winterizing and earlier spring startup. FC was 0 last fall when closed up, and this spring, it had been ice-free for about a month or so before we opened it.

Pool is a 24k IG with SWG. I live in Minnesota, so it freezes hard from about December through March.

[chem geek]

You can prevent this problem by maintaining an FC level in the pool at all times. Obviously you can't easily add chlorine, let alone mix it well, in a pool that is frozen over, so the next best thing is to wait to close the pool until the water temp gets as cold as possible -- at least below 50ºF. At that point, chlorine will last for quite some time so if you close with a shock level of chlorine or even a higher than normal level, it should last through the season. This is especially the case if you use a pool cover that is opaque to sunlight. If your pool is exposed to the sun, then the chlorine will drop even when the water temperature is cooler.

I know that in my own pool the chlorine loss drops to less than 1 ppm FC per week when the water gets to around 50ºF and I suspect that when near freezing the chlorine loss rate is less than half that. However, I have a mostly opaque safety cover.

You should then open the pool before the water warms up, so definitely before it gets above 50ºF.

There are other ways to avoid the problem that involve the use of supplemental products (PolyQuat 60, for example) at extra cost, but the above method using chlorine alone is simple and inexpensive.

[AndyJ]

Thanks, chem_geek. I read the fall closing sticky thread and it said to maintain FC all winter. The author mentioned checking the chlorine periodically throughout the winter and adding it as necessary, but as you mentioned, I couldn't see how that is possible if my pool is frozen solid. I see now that I can just raise it to a high level to last the winter. I do have an opaque auto cover, so that will help prevent FC loss.

However, I also saw mentioned that FC should not be too high, or it might damage my cover, since it will not vent excess chlorine fumes well. I'm guessing a level in the 15 ppm range might be a good medium upon shutting the pump down, say when the water temp is about 40-45.

I did see PolyQuat mentioned as well, so I may give that a try. With your advice, I'm hopeful my situation will be much better next spring. Thanks again.

[chem geek]

Because you'll have CYA in the water, the active chlorine level is actually quite low. Even if your FC were around 40% of your CYA level, the active chlorine (hypochlorous acid) level is the same as found in a pool with 0.6 ppm FC and no CYA. So this is not extraordinarily high. Also, at the much colder temperatures all chemical reactions slow way down.

Nevertheless, to minimize any potential issue, close as late as possible and open as early as possible which is what it sounds like you will be doing. 15 ppm FC with, say, 50 ppm CYA will be like 0.4 ppm FC with no CYA. If you had your CYA higher at 80 ppm that is more typical for SWG pools, then the 15 ppm FC with be like 0.2 ppm FC with no CYA so quite reasonable.