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Thread: FC level increased double what I expected

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    FloridaPoolGal's Avatar
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    FC level increased double what I expected

    Yesterday I added both CL and acid to my pool.

    This is what I posted yesterday on another thread regarding my readings prior to adding anything:

    FC 5.5
    PH 8.0
    TA 110
    CYA ~60

    These are my readings this morning:

    FC 10.0

    CC 0
    pH 7.5
    CH 375 (Note - This is slightly elevated from where we have been because we've tap water 3 times over the last 2 months due to evaporation. We've had windy weather with low humidity.
    H2O 62 degrees

    This is what I added to my approx. 22,000 gallon pool yesterday:

    36 ounces of hydrochloric acid and t
    he pH moved from about 8.0 to about 7.4-7.5
    60 ounces of 10% chlorine and the chlorine moved from 5.5 to 10

    My desire was to increase the FC from 5.5 to 7.5 so I added about 60 oz of 10% chlorine from Home Depot. I used the chart that came in my TF-100 kit to decide how much CL to add (56 oz) and I just went to the Pool Math Calculator and it also says 56 oz.

    How in the heck did I end up with a FC level of 10.0?
    I purchased a case (4 gallons) of the 10% CL from Home Depot about a month ago. Yesterday, I finished the first gallon and started on the second gallon. If anything, I thought CL lost it's potency over time!

    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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    Re: FC level increased double what I expected

    What are you using to test?

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    Mod Squad pooldv's Avatar
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    Re: FC level increased double what I expected

    There are really only a few options.

    You're pool has twice as many gallons
    You added twice as much bleach
    The bleach is twice as strong as advertised
    Test error either before or after addition
    Math error in calculating the test results

    Usually when I get an unexpected outcome it is my fault.
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    Re: FC level increased double what I expected

    Quote Originally Posted by pooldv View Post
    There are really only a few options.
    Quote Originally Posted by pooldv View Post
    You're pool has twice as many gallons
    I think you meant half as many gallons.

    Quote Originally Posted by pooldv View Post
    You added twice as much bleach
    That would be 1 whole bottle.

    Quote Originally Posted by pooldv View Post
    The bleach is twice as strong as advertised
    That would be 20%. Whew! Can bleach fume?

    Quote Originally Posted by pooldv View Post
    Test error either before or after addition
    My personal favorite.

    Quote Originally Posted by pooldv View Post
    Math error in calculating the test results
    10 ml vs. 25 ml test..... hmmmmmmm?

    Quote Originally Posted by pooldv View Post
    Usually when I get an unexpected outcome it is my fault.
    Me too, and I've had some doozies...

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    Mod Squad pooldv's Avatar
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    Re: FC level increased double what I expected

    LOL! Nice!
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    2012 build and pics, 20k gal gunite, black onyx pebblesheen, OK flagstone, IntellifoVS, cart filter w/Pleatco, IC40 SWG, Solartouch, 5 12'x4' solar panels, HP50HA heat pump, 8mil solar cover, borates, TF-100 test kit, SONOS, Doheny's Discovery Robot, hot tub on bleach

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    FloridaPoolGal's Avatar
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    Re: FC level increased double what I expected

    Quote Originally Posted by ewkearns View Post
    What are you using to test?
    TF-100 test kit that is around 60 days old.
    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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    Re: FC level increased double what I expected

    Testing error would be my suspicion..... but, OTOH, assuming the tests *were* accurate, it implies that your pool size is more like 11,000 (Cl) to 15,000 (pH) gallons. Is this the first time you have seen this, or are you just beginning testing?

    You might want to play around with THIS some......

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    FloridaPoolGal's Avatar
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    Re: FC level increased double what I expected

    Quote Originally Posted by pooldv View Post
    There are really only a few options.

    You're pool has twice as many gallons
    You added twice as much bleach
    The bleach is twice as strong as advertised
    Test error either before or after addition
    Math error in calculating the test results

    Usually when I get an unexpected outcome it is my fault.
    The only explanation that makes sense to me is the jug of bleach (2nd one I've used out of the 4 jug carton) is actually double-strength. I just checked that at least the jug says 10% and it does. Jug 2 supplied about 80% of the bleach that I used. Using jug 2 of bleach is virtually the only change from the prior bleach additions to raise the FC so I guess that's where the finger gets pointed.

    I have been testing the CL level every 4-5 days and I have added bleach from jug 1 when necessary. The FC level adjusted to the level that I expected. The second time I did the test this morning, I had my husband watch me because I couldn't believe the results. Today's results do track with what I measured late yesterday so I'm sure the CL level is 10. The Pool Math calculator said I should keep my FC level between 5 and 9 so I guess 10 is not too crazy. My hands smelled of CL after I got done futzing around in the water this morning. I've never experienced that before so something is different.

    Is there any way to test the CL percent in a jug?

    Has anyone ever had something like this happen? It's seems a little far-fetched that one jug of 20% bleach, labeled as 10%, would get mixed with 3 other jugs of 10% bleach. Although, who knows what the other 2 unopened jugs are like.
    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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    Re: FC level increased double what I expected

    Quote Originally Posted by FloridaPoolGal View Post
    Is there any way to test the CL percent in a jug?
    Yes, do a search, here on TFP, but it is kind of a pain and by the time you are diluting to the correct strength, you've lost a lot of accuracy.

    Quote Originally Posted by FloridaPoolGal View Post
    Has anyone ever had something like this happen? It's seems a little far-fetched that one jug of 20% bleach, labeled as 10%, would get mixed with 3 other jugs of 10% bleach. Although, who knows what the other 2 unopened jugs are like.
    You would be hard pressed to find 20% bleach, and even if you did, it wouldn't stay at that strength for long, at all.....

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    Re: FC level increased double what I expected

    Too bizarre!

    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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    Re: FC level increased double what I expected

    Can you do a quick check of the date code on both of the jugs please? I would be curious to see if they are different.

    Kim
    TFP Moderator 33x52 round AG 25,600 gals Sand Filter 1.5hp Pump - 2 Speed, SLAM, Pool School, Recommended Levels, Recommended Chemicals, Pool Math, Chlorine/CYA Chart, TF-100 Test Kit

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    Re: FC level increased double what I expected

    When you used pool math did you chose the 10% bleach option or the 8.25? If you put in 10% bleach bu chose 8.25 in pool math that would account for the increase.....done that myself
    Montgomery, AL
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    Re: FC level increased double what I expected

    Quote Originally Posted by kimkats View Post
    Can you do a quick check of the date code on both of the jugs please? I would be curious to see if they are different.

    Kim
    Good idea!

    Checked the date codes and they are identical. Looks the the bleach has a shelf life to 6-2016.
    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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    Re: FC level increased double what I expected

    Quote Originally Posted by smforte View Post
    When you used pool math did you chose the 10% bleach option or the 8.25? If you put in 10% bleach bu chose 8.25 in pool math that would account for the increase.....done that myself
    I just ran the Pool Math calculator with 10% (56 oz required) and then with 8.25% (65 oz) with a requirement to rasise FC by 2 ppm. The extra 9 oz wouldn't take me from a 2 ppm to a 4 ppm increase in FC.
    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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    Mod Squad kimkats's Avatar
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    Re: FC level increased double what I expected

    All out of ideas! When you go to add it next time put it at 12% and see how far it pushes the FC. Make sure the pump is running to mix it up. Wait about 30 mins. after adding to do the test.

    Hey that made me think of something..........how long after adding the chlorine did you wait to pull the water? Do you always pull the water from the same spot? hummmmmmmm something else to think about.

    Kim
    TFP Moderator 33x52 round AG 25,600 gals Sand Filter 1.5hp Pump - 2 Speed, SLAM, Pool School, Recommended Levels, Recommended Chemicals, Pool Math, Chlorine/CYA Chart, TF-100 Test Kit

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    Re: FC level increased double what I expected

    Quote Originally Posted by FloridaPoolGal View Post
    Good idea!

    Checked the date codes and they are identical. Looks the the bleach has a shelf life to 6-2016.
    Bleach/chlorine does not have a "shelf life", but does have a manufacture date. Generally thery are in a Julian Date format, something like XX16050XXX. In this example teh chlorine was manufactured the 50th day of 2016.

    What is the exact code on your bottle?

    Many times it will leave the plant at a higher concentration than advertised to account for reduction in % in storage and handling. If you get a really fresh bottle it can be higher than listed, but I don't think you will see a 10% bottle with 20% in it.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Mod Squad pooldv's Avatar
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    Re: FC level increased double what I expected

    You got me thinking Kim. Another possibility is the water wasn't fully mixed when the sample was taken. I like that option best.
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    2012 build and pics, 20k gal gunite, black onyx pebblesheen, OK flagstone, IntellifoVS, cart filter w/Pleatco, IC40 SWG, Solartouch, 5 12'x4' solar panels, HP50HA heat pump, 8mil solar cover, borates, TF-100 test kit, SONOS, Doheny's Discovery Robot, hot tub on bleach

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    FloridaPoolGal's Avatar
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    Re: FC level increased double what I expected

    Quote Originally Posted by kimkats View Post
    All out of ideas! When you go to add it next time put it at 12% and see how far it pushes the FC. Make sure the pump is running to mix it up. Wait about 30 mins. after adding to do the test.

    Hey that made me think of something..........how long after adding the chlorine did you wait to pull the water? Do you always pull the water from the same spot? hummmmmmmm something else to think about.

    Kim
    The test that gave me the FC level of 10 ppm was done at least 6 hours after the addition of bleach on Friday, 2/26. I tested Saturday morning, 2/27, and test FC of 10 ppm again. I just re-tested FC and it's at 9.5 ppm.
    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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    FloridaPoolGal's Avatar
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    Re: FC level increased double what I expected

    Quote Originally Posted by tim5055 View Post
    Bleach/chlorine does not have a "shelf life", but does have a manufacture date. Generally thery are in a Julian Date format, something like XX16050XXX. In this example teh chlorine was manufactured the 50th day of 2016.

    What is the exact code on your bottle?

    Many times it will leave the plant at a higher concentration than advertised to account for reduction in % in storage and handling. If you get a really fresh bottle it can be higher than listed, but I don't think you will see a 10% bottle with 20% in it.
    Here are pictures of the bleach bottle to show date code and strength. I now see that the percentage is actually 11% and not 10%. The Pool Math Calculator said it would take 115 oz of 11% bleach to go from a FC level of 5.5 to 10.0. I put in 60 oz on Friday, 2/26/16.
    Attached Images Attached Images
    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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    Re: FC level increased double what I expected

    I rechecked the FC level about 1 pm today, Sunday, 2/28/16:

    FC 9.5 Down .5 from yesterday
    pH 7.5 Same as yesterday

    The pool looks great. The water is clear and sparkling!

    The cat is still drinking the pool water. I hope it's not bad for her but there's no way to keep her from drinking it. Making her stay inside on a beautiful day is not an option because she would meow for hours and scratch at the door and drive her humans CRAZY!
    Approx. 20k gal, kidney-shaped, inground, concrete pool built in 1974. 33' long. 18', 14', & 15' across. 3' to 8' deep. Hayward cartridge filter (c1200e). 1 hp, single speed motor replaced 12/2015. In-line Pentair 320 Chlorine/Bromine feeder (do not use). Screened.

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