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Thread: Very strange chlorine problem

  1. #1
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    Very strange chlorine problem

    I have a very strange problem. Both the total and free chlorine are sky high and remain that way, even if I don't add any chlorine.

    History:
    My pool was green with algae and at the time the PH and alkalinity were both very low (off the scale). I shock treated the pool with 6 cups of granule chlorine and the next day I added 2 Kg (about 4.4 lbs) of "Alkalinity up". After a few days the alkalinity and ph were still extremely low. I then added another 2 Kg of "Alkalinity up" and the alkalinity and ph were now just below normal. The pool however was still green, so I shock treated it again with HTH shock-it which is chlorine based. After this the total chlorine and free chlorine remained super high (off the scale), even after 2 weeks of no chlorine added, in very sunny weather.

    Here are the details:
    Pool volume: 60,000 litres (15,850 US gallons)
    Total hardness: 250 ppm
    Total chlorine: > 10 ppm
    Total Bromine: > 20 ppm
    Free chlorine: > 20ppm
    pH: 7.1
    Total Alkalinity: 70 ppm
    Cyanuric acid: 40 ppm
    Water color: turquiose and very cloudy

    The above were measured using an AquaChek7 strip
    I have confirmed the total chlorine reading using an AquaCheck strip and also an HTH test kit.

    I would appreciate it if someone would please tell me what is happening and what I should do.

  2. #2
    Senior Member Ohm_Boy's Avatar
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    Re: Very strange chlorine problem

    Wow. Where to start...
    Well, foremost, I suspect the test strips to begin with. They are notorious for wildly inaccurate results.
    Also, total chlorine (TC) = free chlorine (FC) + combined chlorine (CC), thus FC cannot be higher than TC, so again, I suspect some error in testing or transcription.
    Moving along...

    Not sure what the composition of the granular chlorine which you first added, but assuming 1) that it was dichlor and 2) that you use 8oz cups, 6cups (48 oz) of Dichlor should have raised the chlorine level of 15,850 gallons of water by over 13000ppm, according to the pool calculator. That is a **VERY** high chlorine level.
    I assume that the HTH shock-it is calcium hypochlorite, and it packs a good concentration of chlorine, but without knowing how much you have added, we cannot estimate what impact it would have had.

    Chlorine will normally drop over time as it is consumed by the sun's UV rays, but the cyanuric acid helps to prevent that loss. Also, 48 ounces of dichlor would have added 12000ppm of CYA, so there may not be a lot of UV loss. It will also drop as it gives up its life fighting organic nasties in the water, but honestly, I cannot conceive of there being any in 13277ppm of FC. I'm at a loss as to how to estimate how long it might take to drop from levels like that. It may make more sense to do a partial drain and refill of the pool water.


    Lastly, that ph of 7.1 is still pretty low, and high chlorine levels will tend to skew ph readings toward the high side, at least the liquid color-comparison tests - not certain about strips, but as mentioned above, we've seen so much error w/ strips that we do not trust them at all. Your ph likely still needs to come up a bit, perhaps to around 7.5 - you'll want to keep a good eye on it as the chlorine levels drop.
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

  3. #3
    Senior Member frogabog's Avatar
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    Re: Very strange chlorine problem

    13000ppm explains it... It'll be down to normal next summer... about August.

    I wonder what the min/max FC is for 12000ppm CYA?

    Sefton, was the granular chlorine dichlor or something else?
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

  4. #4
    Senior Member linen's Avatar
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    Re: Very strange chlorine problem

    Quote Originally Posted by Ohm_Boy
    Not sure what the composition of the granular chlorine which you first added, but assuming 1) that it was dichlor and 2) that you use 8oz cups, 6cups (48 oz) of Dichlor should have raised the chlorine level of 15,850 gallons of water by over 13000ppm, according to the pool calculator. That is a **VERY** high chlorine level.
    Ohm_Boy, I think you used 15 gallons instead of 15000 gallons. From pool calculator for 15000 gallons, starting at 0 ppm FC, adding 48 ounces of dichlor, I get 13 ppm FC and a rise of 12 ppm CYA.

    Quote Originally Posted by sefton

    The above were measured using an AquaChek7 strip
    I have confirmed the total chlorine reading using an AquaCheck strip and also an HTH test kit.
    It seems unlikely that you have any chlorine in there if you have not added any in weeks. Is there a pool store around that you could get an independent test?
    Quote Originally Posted by sefton
    he pool however was still green, so I shock treated it again with HTH shock-it which is chlorine based. After this the total chlorine and free chlorine remained super high (off the scale), even after 2 weeks of no chlorine added, in very sunny weather.
    How much did you add this time? Be careful with this stuff, it adds calcium. What kind of pool surface do you have? Better yet , put your pool/equipment specs in your sig.
    TFP Moderator who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

  5. #5
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    Re: Very strange chlorine problem

    Thanks everyone for the quick and detailed responses, I really appreciate it.
    Quote Originally Posted by Ohm_Boy
    Also, total chlorine (TC) = free chlorine (FC) + combined chlorine (CC), thus FC cannot be higher than TC, so again, I suspect some error in testing or transcription.
    The test strip that I used had a maximum scale of 10ppm for the TC and a maximum scale of 20 for the FC, and in both cases they were off the scale, which is why I quoted TC as >10ppm and FC as >20ppm.

    Quote Originally Posted by Ohm_Boy
    assuming that you use 8oz cups
    Yes the cup is about 8oz.

    Quote Originally Posted by frogabog
    Sefton, was the granular chlorine dichlor or something else?
    I'm not sure what dichlor is, but on the container it says "active ingedient: calcium hypochlorite"

    Quote Originally Posted by linen
    Is there a pool store around that you could get an independent test?
    How much did you add this time?
    What kind of pool surface do you have?
    I will take a sample to a pool store and post the results here - this may take a few days. I added 2 packs of shock-it, and I would guess that they were about 1.5 lbs each. I will check the next time I'm at the store. The pool surface is fibreglass - I think

  6. #6
    Senior Member linen's Avatar
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    Re: Very strange chlorine problem

    Yeah, the test strips tend to be useless. I would get a good test kit (see my sig). 3 lbs of 48% cal-hypo would only raise FC by 11. My guess is you have no FC in the pool now, I would dose it using bleach/liquid chlorine using the poolcalculator.com. See: http://www.troublefreepool.com/pool-...king_your_pool. However, to continue the shocking process, you will need a good test kit.
    TFP Moderator who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

  7. #7
    Senior Member Ohm_Boy's Avatar
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    Re: Very strange chlorine problem

    Ohm_Boy, I think you used 15 gallons instead of 15000 gallons. From pool calculator for 15000 gallons, starting at 0 ppm FC, adding 48 ounces of dichlor, I get 13 ppm FC and a rise of 12 ppm CYA.
    Whew! That is a good thing. I copied and pasted the 15,850 from the OP into the poolcalc, and while I did think that was kinda high for an FC value, I didn't go back and check.
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

  8. #8
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    Re: Very strange chlorine problem

    Quote Originally Posted by linen
    Yeah, the test strips tend to be useless. I would get a good test kit (see my sig).
    The only test kits that I have seen here is the HTH kit, which I have and it agrees with the test strips. It is however a fairly basic kit. I will do what you suggested and take a sample to a pool centre.

  9. #9
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    Re: Very strange chlorine problem

    With a 15,000 gallon pool it would be worth the trouble and expense to get a good test kit. Since you quoted your volume in litres I'm going to assume you're not in the US so that makes it a little harder and more expensive to find a good kit. Look for a K-2006 if you're in Canada or a Palintest 315C elsewhere.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 1.5hp Dynamo pump. 24" Pentair Sand Dollar Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit
    You can stop SLAMing your pool when you pass the OCLT (You lose 1ppm or less FC overnight, & You have .5ppm CC's or less) & your water is clear.

  10. #10
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    Re: Very strange chlorine problem

    Dave, I'm in South Africa, and I havent actively gone looking for a good kit, but the only one that I have noticed in the stores is the HTH kit, which is a fairly basic kit.
    By the way, my pool has now turned blue and is starting to clear up, without having put any more chemicals in. Maybe I should patent this "problem"

    For the record, I phoned up a pool place that offers free water testing and asked how they test the water. They told me that they use a strip, so I didn't bother taking in a sample.

  11. #11
    Senior Member frogabog's Avatar
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    Re: Very strange chlorine problem

    Maybe the pool store can special order you a Taylor K-2006 kit?

    Or, perhaps TFTestkits.net knows of a solution. I'd contact them and ask for advice. You can use the contact form/page on the website to send an email.
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

  12. #12
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    Re: Very strange chlorine problem

    I've had a look on amazon.com, and they have a whole range of kits, so I will order one.

  13. #13
    Administrator Leebo's Avatar
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    Re: Very strange chlorine problem

    http://www.amazon.com/gp/aw/d/B0002IXII ... 329&sr=8-1

    Amazon carries K-2006 for you. Not sure on shipping rates for you.

  14. #14
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    Re: Very strange chlorine problem

    Thanks Leebo

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