Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 14 of 14

Thread: FC drop

  1. Back To Top    #1
    dabuddy's Avatar
    Join Date
    Jul 2008
    Location
    Grand Rapids, MI
    Posts
    97

    FC drop

    Hey guys, member me? I did the Bacqua-goo conversion a couple of weeks ago, went on vacation and now back and maintaining my crystal clear pool. I have a question about my FC consumption. I understand that FC is only consumed by sunlight or organic matter.

    Sunday when I returned from vacation my CC was 0.5 (6 PM) and yesterday (Monday 8 PM) my CC wasto 1.0 so I brought my pool to shock level last night (FC 16.5 - took reading about 1/2 hour after adding bleach). ph 7.2, CYA 60.

    This morning when I woke up I did a reading and my FC was 18.0 (actually went up!) CC was 0.2 (very very light pink; I don't think I needed a full drop to bring it back to clear so I estimate 0.2). pH 7.2. When I got home today from work I took a reading and my FC dropped to 8.0 and CC was 0.5. Swimmer load today was 3 teens for 2 hours and they didn't splash enough to raise the pH.My question/concern, with a CYA of 60 and FC of 18.0 this morning is it normal to drop 10 ppm today over a 12 hour period?

    What should my actions be, wait, shock, other?

    I just added 4 lbs, 12 oz of Borax just now to try to get pH up from 7.2 to 7.5.
    Chris

    18'x36' (Depth: deep 8'6" shallow 3'6") rectangular 27,000 Gallon Vinyl In Ground. Hayward self-priming super pump 1 HP 2600x5-96, Hayward Pro Series High Rate 24" 7-Position 300 lb Sand Filter, Hayward H250 Natural Gas 250,000 BTU Electronic Ignitiion - Digital Readout Heater, Hayward Navigator 925V PoolVac.

    Converted Baquacil to Chlorine - should have done it sooner!

  2. Back To Top    #2
    frustratedpoolmom's Avatar
    Join Date
    May 2007
    Location
    SWSuburban Chicago, IL
    Posts
    11,963

    Re: FC drop

    I would say that's probably within normal limits....best way to check is to do an overnight comparison. Record tonights result, and compare it in the morning, see if your FC is holding in the dark....
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

  3. Back To Top    #3
    TizMe's Avatar
    Join Date
    Aug 2007
    Location
    Covington, Georgia
    Posts
    920

    Re: FC drop

    The following are some quotes taken from other threads about FC loss:

    Quote Originally Posted by JasonLion
    Sunlight losses are a percentage, so you lose more the higher the initial level. Disinfection loses are constant relative to the starting level, so it doesn't matter what you starting level is. For most pools sunlight loses predominate, but a heavy bather load could make the disinfection losses significant. There are some more complex effects if your level is low enough to allow algae to get started.

    Quote Originally Posted by mas985
    Chemgeek will probably correct me if I am wrong but first order extinction rates are based primarily upon the percentage of chlorine. So for example at a CYA of 30 ppm, I lose about 50% of the chlorine during the day. It doesn't seem to matter much what the level starts at but the extinction rate of 50% is pretty constant.

    However, what I have found is that if you double the CYA, the extinction rate goes down by more than 50% so you come out ahead with higher CYA.
    Les
    Don't have a pool right now. Just sharing what I have learned over the years!
    Helpful Links:
    Pool School,Pool Calculator,Cl/CYA Shock Chart,TF Test Kit
    Doing BBB and loving it!

  4. Back To Top    #4
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,887

    Re: FC drop

    Chlorine loss to sunlight should have been 30-40%, call it 6 ppm. But you also had six person hours of swimming, which is a significant bather load. That could easily account for the other 4 ppm lost.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  5. Back To Top    #5
    dabuddy's Avatar
    Join Date
    Jul 2008
    Location
    Grand Rapids, MI
    Posts
    97

    Re: FC drop

    Thanks guys for the quick and clear responses. I'm still learning but I get it...
    Chris

    18'x36' (Depth: deep 8'6" shallow 3'6") rectangular 27,000 Gallon Vinyl In Ground. Hayward self-priming super pump 1 HP 2600x5-96, Hayward Pro Series High Rate 24" 7-Position 300 lb Sand Filter, Hayward H250 Natural Gas 250,000 BTU Electronic Ignitiion - Digital Readout Heater, Hayward Navigator 925V PoolVac.

    Converted Baquacil to Chlorine - should have done it sooner!

  6. Back To Top    #6
    dabuddy's Avatar
    Join Date
    Jul 2008
    Location
    Grand Rapids, MI
    Posts
    97

    Re: FC drop

    ph looks to be about 7.7 now.
    Chris

    18'x36' (Depth: deep 8'6" shallow 3'6") rectangular 27,000 Gallon Vinyl In Ground. Hayward self-priming super pump 1 HP 2600x5-96, Hayward Pro Series High Rate 24" 7-Position 300 lb Sand Filter, Hayward H250 Natural Gas 250,000 BTU Electronic Ignitiion - Digital Readout Heater, Hayward Navigator 925V PoolVac.

    Converted Baquacil to Chlorine - should have done it sooner!

  7. Back To Top    #7
    dabuddy's Avatar
    Join Date
    Jul 2008
    Location
    Grand Rapids, MI
    Posts
    97

    Re: FC drop

    Readings:

    10 PM last night:
    FC - 10.5
    CC - 0.5 (very, very light pink though)
    TC - 11.0
    pH - 7.7

    7 AM this morning:
    FC - 10.5
    CC - 0.5 (very, very light pink though)
    TC - 11.0
    pH - 7.7

    This is my baseline for finding out how much FC I lose today due to sunlight and bather load.
    Chris

    18'x36' (Depth: deep 8'6" shallow 3'6") rectangular 27,000 Gallon Vinyl In Ground. Hayward self-priming super pump 1 HP 2600x5-96, Hayward Pro Series High Rate 24" 7-Position 300 lb Sand Filter, Hayward H250 Natural Gas 250,000 BTU Electronic Ignitiion - Digital Readout Heater, Hayward Navigator 925V PoolVac.

    Converted Baquacil to Chlorine - should have done it sooner!

  8. Back To Top    #8
    TizMe's Avatar
    Join Date
    Aug 2007
    Location
    Covington, Georgia
    Posts
    920

    Re: FC drop

    I think a CC of 0.5 can be ignored because sometimes even though the water appears clear with a pink haze sometimes that extra drop will make it actually turn clear. I always miss that extra drop when I'm testing!
    Also IF after adding your drops you let it sit a few minutes and thrn looked at it again it will turn slightly pink
    Les
    Don't have a pool right now. Just sharing what I have learned over the years!
    Helpful Links:
    Pool School,Pool Calculator,Cl/CYA Shock Chart,TF Test Kit
    Doing BBB and loving it!

  9. Back To Top    #9

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,085

    Re: FC drop

    If in doubt, you can use a 25 ml water sample instead of 10 ml and then each drop of titrant will represent 0.2 ppm instead of 0.5 ppm.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  10. Back To Top    #10
    dabuddy's Avatar
    Join Date
    Jul 2008
    Location
    Grand Rapids, MI
    Posts
    97

    Re: FC drop

    Cool, next time I do the test I'll use a 25ml sample.

    In case anyone is wondering, my readings at 8:30 PM today after 2 swimmers for 2 hours and mostly overcast all day (sun came out mid-afternoon):

    FC - 4.5
    CC - 0.5 (very, very light pink though)
    TC - 5.0
    pH - 7.6
    Chris

    18'x36' (Depth: deep 8'6" shallow 3'6") rectangular 27,000 Gallon Vinyl In Ground. Hayward self-priming super pump 1 HP 2600x5-96, Hayward Pro Series High Rate 24" 7-Position 300 lb Sand Filter, Hayward H250 Natural Gas 250,000 BTU Electronic Ignitiion - Digital Readout Heater, Hayward Navigator 925V PoolVac.

    Converted Baquacil to Chlorine - should have done it sooner!

  11. Back To Top    #11
    Butterfly's Avatar
    Join Date
    May 2007
    Location
    South Carolina
    Posts
    10,045

    Re: FC drop

    Quote Originally Posted by dabuddy
    Cool, next time I do the test I'll use a 25ml sample.

    In case anyone is wondering, my readings at 8:30 PM today after 2 swimmers for 2 hours and mostly overcast all day (sun came out mid-afternoon):

    FC - 4.5
    CC - 0.5 (very, very light pink though)
    TC - 5.0
    pH - 7.6
    Okay, unless I missed something, your CYA is still 60? Then your MINIMUM FC should be 5 and you just reported 4.5ppm. With a CYA of 60, your Min is 5 & Target is 7 to 9, so you are going to have to add enough chlorine each evening to keep you above your minimum FC between doses! You may have to shoot for 10 or 12, depending on your pool's daily use (organics, bather load, sun, etc.) so that you do not drop too low.

    It is not a good idea to get too close to your Min FC for your CYA, it can bite you when you least expect it! (Don't ask me how I know this )

    So, what did you increase your FC to tonight?
    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!

  12. Back To Top    #12
    dabuddy's Avatar
    Join Date
    Jul 2008
    Location
    Grand Rapids, MI
    Posts
    97

    Re: FC drop

    Yup, CYA is still 60. i get FULL sun all day. I was shooting for 10 FC tonight. Since I don't want to drop below 5 perhaps I can yank the kids out a 1/2 hour earlier tomorrow!

    I added 2.25 gallons according to the PoolCalculator to get it from 4.5 to 10. With your advice I will now get it to 12. I just added 3/4 more gallons. I ran out of R-0871 so I now am guessing I ordered replacement Sunday night so I should get it soon.

    Thanks a bunch for your advice!
    Chris

    18'x36' (Depth: deep 8'6" shallow 3'6") rectangular 27,000 Gallon Vinyl In Ground. Hayward self-priming super pump 1 HP 2600x5-96, Hayward Pro Series High Rate 24" 7-Position 300 lb Sand Filter, Hayward H250 Natural Gas 250,000 BTU Electronic Ignitiion - Digital Readout Heater, Hayward Navigator 925V PoolVac.

    Converted Baquacil to Chlorine - should have done it sooner!

  13. Back To Top    #13
    Butterfly's Avatar
    Join Date
    May 2007
    Location
    South Carolina
    Posts
    10,045

    Re: FC drop

    So glad you added some more! Sure don't want you to yank the kids out early!
    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!

  14. Back To Top    #14

    Re: FC drop

    Quote Originally Posted by dabuddy
    perhaps I can yank the kids out a 1/2 hour earlier tomorrow!
    yea, good luck with THAT one!!

    8000 gallon 20' x 48" round vinyl frame pool, 12" sand filter (don't have the specs on the pump), TF100 test kit
    Handy Links: PoolMath, TF-100 Test Kit, Pool School, CYA-Chlorine Chart
    "Shock" is a process, not a product!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •