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Thread: Is it normal to see huge swings in FC/CC?

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    Is it normal to see huge swings in FC/CC?

    I'm starting to think I don't know how to do the DPD test, although when I get an unusual result, I typically pull another sample from a different part of the pool and it always comes out the same.

    Anyway, I've been shocking my pool for a week now...I haven't done the best job of it because I've got 3 kids, a full time job, and my wife was running in the election last week so pool time was at a premium. posting.php?mode=post&f=10#

    Anyway, I'm getting what seems to me to be some crazy results on the FC/CC test and I'm wondering if I'm doing it wrong.

    Here's an example...I tested after dark on Friday night...FC=15, CC=0. Brushed the heck out of the pool. Went to bed. Saturday morning I tested at 9am and got FC=2.5, CC=12.5. Holy **** that is a big swing, but I guess it kind of makes sense if I'm fighting a lot of algae. So I ran to the pool calculator and it told me to use 2.3 gallons of my 10% bleach to get back to shock level. So I added 2 gallons (not 2.3) and then headed out with the family. Didn't get back until 2pm. Tested @ 2pm and got FC=22.5, CC=1.5! There's no way 2 gallons of bleach could raise my FC 20 ppm. I pulled more water and got the same result. The filter has been running 24/7, and I'm pulling from several inches under the surface.

    The same thing happened Sunday...I tested in the morning and found FC=5, CC=20! Put 2 gallons of bleach in and a few hours later I got FC=25. Now I'm freaking out that I'm going to bleach my liner worse than it already is (previous owners did a number on the 10 year old liner already).

    1 question I have on the DPD test...sometimes when I test FC, the water turns completely clear. So I put the lid on the dropper and reach for the R0003 reagent and by the time I do, the water is back to a very slight pink. I know I've read that the water will turn back to pink if you wait a while, but this is only a matter of 10 seconds. Is that the problem?
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

  2. Back To Top    #2

    Re: Is it normal to see huge swings in FC/CC?

    Oh, I should add that my water is very clear with a mint green tint to it. I still have slight clouds of algae on the bottom when I brush. The clouds are lessening, but the tint doesn't seem to be changing. If my FC was really this high, I'd have thought the water would have cleared by now. But it is hard to properly shock when you don't trust your test results.

    I've got a brand new TF100...so quality and age of testing agents are not an issue.
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

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    Join Date
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    Re: Is it normal to see huge swings in FC/CC?

    do you have the speed stir?
    8,000 gallon, in ground, fiberglass pool with a cartridge filter.

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    Re: Is it normal to see huge swings in FC/CC?

    Speed stir is coming in the mail...hopefully today!
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

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    linen's Avatar
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    Re: Is it normal to see huge swings in FC/CC?

    Quote Originally Posted by brian4110
    I'm starting to think I don't know how to do the DPD test,
    I assume you mean the fas-dpd test not the dpd test? The fas-dpd test uses R-0870 and R-0871 reagents.
    TFP Expert 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.

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    Re: Is it normal to see huge swings in FC/CC?

    Yes, sorry...FAS-DPD is exactly what I am talking about. Those are the reagents.
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

  7. Back To Top    #7
    linen's Avatar
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    Re: Is it normal to see huge swings in FC/CC?

    It is possible that you may not be putting in enough of the powder then. Take a look at the extended test kit instructions: http://www.troublefreepool.com/exten...1.html#p206393

    Out of curiousity, did you lose a lot of cya over the winter this year?
    TFP Expert 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.

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    Re: Is it normal to see huge swings in FC/CC?

    Can you post a full set of test results?

    What was the CYA level when you closed your pool last year?
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  9. Back To Top    #9

    Re: Is it normal to see huge swings in FC/CC?

    I opened to zero CYA this year and I did not own the pool at closing, so I have no idea how much I may have lost. HOWEVER...I did inherit half a bucket of trichlor pucks, a half bucket of CYA, and a few bags of cal-hypo from the previous owners, so I assume there was at least some CYA in at close! My CH is running at 340, so I suspect the previous owners used mostly the cal-hypo for chlorinating so the CYA was probably not sky high. At opening, the bottom of the pool was really filthy with dirt and mulch blown in from poolside over the winter. I've previously been advised that I probably don't have an ammonia problem because it is rare.
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

  10. Back To Top    #10

    Re: Is it normal to see huge swings in FC/CC?

    I didn't have a chance to test this morning...it was raining pretty hard and I was in a rush. My last test result is from midnight last night...(wont be back home to test until tonight - work and kids' baseball games)

    FC = 20
    CC = 6
    pH = 7.6 (haven't tested since I started shocking...this was pre-shock)
    CH = 340
    CYA = 20
    TA = 90
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

  11. Back To Top    #11
    linen's Avatar
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    Re: Is it normal to see huge swings in FC/CC?

    It seems possible that you are fighting ammonia caused by the breakdown of cya over the winter by bacteria.

    The good news is the shocking process will take care of it...that bad news is that ammonia takes a lot of chlorine to neutralize.

    If you want, you could pick up an ammonia test for fish tanks at a pet store and test for it. Not required though.
    TFP Expert 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.

  12. Back To Top    #12

    Re: Is it normal to see huge swings in FC/CC?

    Would that cause the huge swings? I would think ammonia might be the cause of the huge CC numbers I sometimes get, but I have no idea why my FC goes through the roof sometimes after I add a poolcalculator appropriate amount of bleach. I have a hard time believing I am screwing up the testing so badly.

    Also, any idea what is causing the continued green tint to my water? It is almost indistiguishable in the shallow end, but defintely noticeable in the deep end. I can easily and clearly see the bottom in the deep end though.
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

  13. Back To Top    #13
    Butterfly's Avatar
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    Re: Is it normal to see huge swings in FC/CC?

    I suggest you go ahead and add enough CYA to reach 30 for now to help with the shock process.

    We understand the difficulty of shocking on a limited schedule. As long as you raise to shock level every morning and as many times in the evening as you can squeeze in (2 minimum ) it will clear in time.

    If you give us a walk-thru on how you are using the Pool Calculator to get your doses, we'll give that a look-see. ie, what are you putting in "Now" & what are you putting in "Target" and what size pool/gallons are entered?

    Once you get thru this, maintaining your pool will be a breeze
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

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    Re: Is it normal to see huge swings in FC/CC?

    Green tint in water, gave you tested for copper or iron?
    Southern NJ, 1 HP Haward Pump, 16x 32 dimensions, 21,000 gallon vinyl liner inground pool, TF-100 test kit.

  15. Back To Top    #15

    Re: Is it normal to see huge swings in FC/CC?

    I have not tested for metals. I am 100% sure the pool was filled with city water. No idea how long ago.
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

  16. Back To Top    #16
    Butterfly's Avatar
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    Re: Is it normal to see huge swings in FC/CC?

    Can you post a pic of the pool?
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  17. Back To Top    #17

    Re: Is it normal to see huge swings in FC/CC?

    Quote Originally Posted by Butterfly
    If you give us a walk-thru on how you are using the Pool Calculator to get your doses, we'll give that a look-see. ie, what are you putting in "Now" & what are you putting in "Target" and what size pool/gallons are entered?
    I have a 27,500 gallon pool. I'm pretty confident in this number as I have the original paperwork from when the pool was built (this is the number in the paperwork) and it checks out when I punch in the dimensions.

    At my level of CYA, the pool calculator says I need to shock at 11 FC. The other morning I tested and found FC had fallen to 2.5 overnight (again...my testhttp://www.troublefreepool.com/post ... &p=499141#). I punched 2.5 into the current FC side and 11 into the target and it suggested I add 2.3 gallons of 10% liquid chlorine. I'm using the HTH brand from Walmart. I added 2 gallons. Went back out later in the day to test and FC read over 20. According to the PC, 256 oz of chlorine should only have raised FC by 7.3.

    I know what you are thinking...this guy either doesn't know how to count drops and divide by 2, or he doesn't know how to count bottles of bleach! Everytime I get a crazy result, I retest only to find the same result. I can only assume user error, but I am doing everything in my power to eliminate that possibility.
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

  18. Back To Top    #18

    Re: Is it normal to see huge swings in FC/CC?

    Quote Originally Posted by Butterfly
    Can you post a pic of the pool?
    Absolutely...but not until tonight.
    18' x 41' IG w/vinyl liner. 30000 Gallons. 78" x 78" poolside spa
    1.5 hp Hayward pump - sand filter & Tiger Shark QC robot
    Compool CP3800 Control Panel
    TF-100 kit
    Built in 2002. "Inherited" w/House in 2012. Located in Pittsburgh

  19. Back To Top    #19
    Butterfly's Avatar
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    Re: Is it normal to see huge swings in FC/CC?

    Quote Originally Posted by brian4110
    Quote Originally Posted by Butterfly
    If you give us a walk-thru on how you are using the Pool Calculator to get your doses, we'll give that a look-see. ie, what are you putting in "Now" & what are you putting in "Target" and what size pool/gallons are entered?
    I have a 27,500 gallon pool. I'm pretty confident in this number as I have the original paperwork from when the pool was built (this is the number in the paperwork) and it checks out when I punch in the dimensions.

    At my level of CYA, the pool calculator says I need to shock at 11 FC. The other morning I tested and found FC had fallen to 2.5 overnight (again...my testhttp://www.troublefreepool.com/post ... &p=499141#). I punched 2.5 into the current FC side and 11 into the target and it suggested I add 2.3 gallons of 10% liquid chlorine. I'm using the HTH brand from Walmart. I added 2 gallons. Went back out later in the day to test and FC read over 20. According to the PC, 256 oz of chlorine should only have raised FC by 7.3.

    I know what you are thinking...this guy either doesn't know how to count drops and divide by 2, or he doesn't know how to count bottles of bleach! Everytime I get a crazy result, I retest only to find the same result. I can only assume user error, but I am doing everything in my power to eliminate that possibility.
    Yep, Pool Calculator info is confirmed with your numbers So, I guess there could possibly be some user error.

    Would you give us a walk-thru on how you are doing the FAS/DPD test?
    Some folks have been known to use 25ml water and test as 10ml. Don't ask me how I know this
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  20. Back To Top    #20
    Casey's Avatar
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    Re: Is it normal to see huge swings in FC/CC?

    Maybeeeeee.... the pool isn't as big as what the paper work says it is? Could it be? If you are over shooting the chlorine, it could be possible. Yes?
    I'd bet you my bikini you'll never get TFP water from a pool store!

    24' Sharkline Venture De Filter

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