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How To Lower Combined Chlorine


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#1 meyergsr

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Posted 23 April 2007 - 03:34 PM

Hello, New owner with question about lowering combined chlorine. My tub is about 3 weeks old and 330 gal with no ozone installed. I have been using bleach to keep the FC around 4 or 5, my total alkalinity is 80, PH is 7.6 and CYA is less then 30. I usually put in around a 1/2 cup of bleach after use. I shocked with chlorine a couple of times to remove CC which is around 1.0 right now the first time I shocked with 2 cups and second time I shocked with 2.5 cups. I am testing with the Taylor 2006 kit. Should I be shocking with MPS instead of bleach to remove the CC or use more then 2.5 cups of bleach(regular chlorox)?

#2 waterbear

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Posted 23 April 2007 - 09:54 PM

If you still have combined chlorine after shocking then you haven't reached 'breakpoint'. Are you keeping the cover off when you shock and is the spa exposed to sunlight? Both of those are important to break down the combined chlorine. How high are you raising the free chlorine when you shock. Try raising it to 20 or 25 ppm with the cover off in the evening and leave it uncovered all night and day. Check your chlorine the next evening. 2.5 cups of bleach should raise your free chlorine about 25 ppm. MPS will not break down combined chlorine as effectively as chlorine can and will test as combined chlorine in your water unless you get the special reagent from Taylor to remove the interferance.
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#3 meyergsr

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Posted 24 April 2007 - 03:33 AM

If you still have combined chlorine after shocking then you haven't reached 'breakpoint'. Are you keeping the cover off when you shock and is the spa exposed to sunlight? Both of those are important to break down the combined chlorine. How high are you raising the free chlorine when you shock. Try raising it to 20 or 25 ppm with the cover off in the evening and leave it uncovered all night and day. Check your chlorine the next evening. 2.5 cups of bleach should raise your free chlorine about 25 ppm. MPS will not break down combined chlorine as effectively as chlorine can and will test as combined chlorine in your water unless you get the special reagent from Taylor to remove the interferance.


Hi waterbear, I left the cover off for around 15min with the jets on when shocking. I did not test after adding the shock, but like you said it should have been high enough to reach the breakpoint. The spa is under a roof and does not get any sunlight. I guess I will try leaving the cover off longer. Should the pumps be on during this shock?

#4 waterbear

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Posted 24 April 2007 - 09:07 AM


Hi waterbear, I left the cover off for around 15min with the jets on when shocking. I did not test after adding the shock, but like you said it should have been high enough to reach the breakpoint. The spa is under a roof and does not get any sunlight. I guess I will try leaving the cover off longer. Should the pumps be on during this shock?

Yes, have your circulation going when you shock and level the cover off until the chlorine level drops to normal. Shock at night and try to leave the cover off for most of the next day and see if you killed the Combined Chlorine.

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