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Strange Chlorine Problem After Shocking


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Thank you for any help on this question. I have a salt water in-ground pool which had an algae bloom, due to me lowering the generator down to "1" when it got cold out. Next time I will run for fewer hours and leave it at "2" where it normally is. I shocked the pool with 2 jugs of liquid chlorine that had been sitting in my garage about a year and it did not work. All the while cleaning the filter daily, even bought a new filter just to be sure. After about a week Free chlorine was about 10 and Total chlorine about 3. Yes you read that correctly. I figured I had a problem and bought 2 bags of crystalized shock and threw them in there at nighttime, ran for 24 hours, everything cleared up, crystal clear. Ever since the Free chlorine has been around 20 and Total chlorine about 10. After about 4-5 days when it wouldn't drop I turned off the generator altogether. its been about another 4-5 days and we are down to about Free Chlorine 10 total Chlorine 5. Has anyone ran into anything like this before? I have tested with the test strips which give a separate reading for Free and total chlorine, since the dropper method has you simply wait longer to get Total chlorine it wouldn't ever give a reverse reading like I am seeing. Thank you in advance, I am starting to get concerned.

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Chlorine loses its strength so after one year it may not have been very strong.

It sounds like you are using test strips. They are next to useless as you have found out since it is impossible for Total Chlorine to be lower than Free Chlorine. You should get a proper test kit -- the Taylor K-2006 with its FAS-DPD chlorine test. Do not get the K-2005 or other DPD test as these are not as accurate and they bleach out at high chlorine levels.

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If the pool is covered then uncover it to expose it to sunlight as that should lower the FC faster. If there is no sunlight, then you can lower the chlorine level with a chlorine neutralizer, but if you have a high Cyanuric Acid (CYA) level then a higher FC is not a problem and the active chlorine level may be quite low as that is proportional to the FC/CYA ratio. For example, if you had a CYA of 100 ppm then 10 ppm FC would be the same as having only 3 ppm FC with 30 ppm CYA.

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If the pool is exposed to sunlight and the chlorine is not dropping then that is unusual, but perhaps the Cyanuric Acid (CYA) level is very high. If that is the case, you should consider a partial drain/refill to lower it since it's just going to cause you problems down the road. Your CYA shouldn't be above 80 ppm for a saltwater chlorine generator pool.

What was the "crystalized shock" that you used? I suspect that instead of being Cal-Hypo it might have been Dichlor. For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

You can dilute your water sample with distilled water (or tap water if you measure the chlorine in the tap water separately to account for it) to see your chlorine level. If it's only near 10, just leave it as it should continue to drop and if the CYA level is high than 10 ppm FC is not a problem. If it's much higher than 10 then yes you can get a chlorine neutralizer from your pool store.

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  • 2 weeks later...

ok so I got the neutralizer. It brought the chlorine in the pool to zero. I immediately turned the generator back on, and set it to "4" to make sure the chlorine would come back up. After several days of reading "0", I finally read a "2" this morning, perfect. So I set the generator to "2" and let it run the rest of the day. I just tested the water now and we are back to "10-20". Why is this happening???

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You have the generator set up to high. At this time of year chlorine demand is much, much lower because the water temperature is colder and there is less sunlight on the pool. Set your saltwater chlorine generator on-time to a lower setting (perhaps the lowest of "1" and if necessary lower your pump run time as well since it is the product of the SWCG setting and the pump run time that determines the amount of chlorine it adds to the pool.

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  • 2 weeks later...

OK so its been like 6 weeks since shocking and the chlorine still won't go down. This is INSANE. This is the shock I used: http://www.homedepot.com/p/Pool-Time-1-lb-Shock-PLUS-4-in-1-Pool-Shock-22816PTM/100003536 I lowered the generator to "1" and only ran it 4 hours a week for a week and just got back to down and the chlorine is still too high to use the pool. I am thinking I will have to drain it and start over, because I am at my wit's end.

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You could shut off the SWG completely but if you want the chlorine to go down faster you can always add a chlorine neutralizer. However, how high is your FC level? And what is your CYA level? With CYA in the water, I doubt very much that your FC is actually too high since the active chlorine level is proportional to the FC/CYA ratio.

This is especially true since the shock you used was Dichlor so for every 10 ppm FC added it also increases CYA by 9 ppm.

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