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Thread: FC question

  1. Back To Top    #1

    Join Date
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    FC question

    I have been using trichlor pucks over the summer (a lot of travel) and managed to get my CYA levels over 100. The other day we had several days of rain resulting in a little bit of green film around the tile which looked like algae (I am sure it was). FC tested around 6.6 however knowing that my CYA levels were so high, I suspected the algae was a result of lower than effective levels of FC given my CYA level and the rain. I brushed down the pool, ran filter overnight with the inline chlorinator opened wide and the slight green film resolved. I decided to stop using trichlor and used bleach.

    According to pool math calculator, to get FC to 11 (given the CYA level), I needed to add about 128 oz 8.25% bleach to my 19k gallon pool. I added 121 oz. Now my FC level is well over 50 the next day. 48 hours later it remains more than 50.

    I did have my CYA levels checked twice prior to adding the bleach.

    I would Appreciate any input on how I could overshoot from FC goal of 11 to more than 50 with 1 gallon of bleach. I did confirm that it was 8.25% bleach and I did test FC more than once (before and after treatment)

    Yes, I do plan to drain half the pool this weekend to correct CYA levels.

    Thanks

  2. Back To Top    #2
    Mod Squad tim5055's Avatar
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    Re: FC question

    There is no way it could happen. There is not sufficient chlorine in the bottle to get the FC that high.

    Pool Math says to go from 6.6 to 50 you would need 1,244 oz of 8.25% bleach.

    What test kit are you using??

    It would help us if you would add your location to your profile and add the following information to your signature


    • The size of your pool in gallons
    • If your pool is an AG (above ground) or IG (in ground)
    • If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass
    • The type of filter you have (sand, DE, cartridge) and, if you know, the brand and model of the filter.
    • If you know, please tell us the brand and model of the pump, and mention if is it a two speed or variable speed pump.
    • Date of pool build/install, particularly important if less then a year old.
    • What kind/model of water test kit you are using
    • Other significant accessories or options, such as a spa , SWG, or cleaner
    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 jblizzle's Avatar
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    Re: FC question

    Please add your location (City, State or City, Country) to your profile and pool details to your signature as described HERE as it will help us help you.

    I agree with Tim ... what you described is not possible. I would suspect testing error.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
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  4. Back To Top    #4

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    Re: FC question

    Taylor fas dpd. I even ran it on a second basic pentair OTO test and with 1 drop, it turned bright yellow suggesting high chlorine levels

  5. Back To Top    #5
    Mod Squad tim5055's Avatar
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    Re: FC question

    If you are using a TF-100 or a K-2006 (taylor based test kit) it appears you are using 25 mL sample for 0.2 ppm accuracy. You =can go ahead and use 10 mL sample for 0.5 ppm accuracy. It will save you reagents and is close enough for us.

    But for your test to test 50ppm you would have used 250 drops of reagent to change the sample from red to clear. Did you use 250 drops?
    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 jblizzle's Avatar
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    Re: FC question

    The OTO test does not work that way. What does it look like with 5 drops?

    Describe how you are doing the FAS-DPD test.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
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  7. Back To Top    #7
    pwrstrk's Avatar
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    FC question

    Pool Math states one jug of bleach 121oz will raise FC by 4.2 in a 19k gallon pool. At the bottom of the page Effect Of Adding Chem's.
    Something is amiss here.
    If you could add all your pool, equipment and location to your sig, that will help us help you better. 😎
    Jeff
    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

  8. Back To Top    #8

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    Re: FC question

    Sorry guys, I updated my info. New build as of 3/2014. 19k gallons, pebble sheen, pentair VS pump with Quad DE filter

    Live in central Texas. Not really new to testing pool water as I did it as a kid growing up and have been doing it regularly this year

    When 5 drops were added to the OTO, it turned orange tinted after passing through yellow with the first couple of drops. I will test again tomorrow evening with FAS DPD. Using 10 ml sample
    19k gallon pool with attached spa, in ground, pentair VS pump, Quad DE filter, Pebble Sheen plaster, built 3/2014

  9. Back To Top    #9
    Mod Squad tim5055's Avatar
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    Re: FC question

    Quote Originally Posted by jms View Post
    When 5 drops were added to the OTO, it turned orange tinted after passing through yellow with the first couple of drops.
    Well, here is a quote from Richard320:

    Quote Originally Posted by Richard320 View Post
    On the OTO (yellow) chlorine test:

    Blinding tweety-bird yellow is about 10. School bus yellow is about 12-13. Hunter orange is around 18, up around 25 it starts to look pumpkin orange.
    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

  10. Back To Top    #10

    Re: FC question

    Test error seems likely. However, if the FC really did jump up much more than expected, I would suspect that the tab feeder had been filled with tabs and the dial was set too low to allow good flow. The tabs could have dissolved in the feeder, and when you opened it all of the way, the concentrated chlorine was allowed out.

    Quote Originally Posted by jms View Post
    I brushed down the pool, ran filter overnight with the inline chlorinator opened wide and the slight green film resolved.

  11. Back To Top    #11

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    Re: FC question

    The main problem here is that your CYA is off the charts. You need an accurate measure of your CYA using a dilution test to determine where you are. The only way you are going to resolve your problems long term is to determine your CYA level, drain and refill pool with enough water to get you to ~40ppm CYA and then SLAM and rebalance your pool water.

    Any further bleach dumping is going to be a waste of your time and money.

    Long term you need to remove the tab feeder and install either a bleach Stenner pump or an SWCG.



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