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Thread: CYA disappears

  1. Back To Top    #1

    Join Date
    Apr 2009
    Location
    Central Minnesota
    Posts
    74

    CYA disappears

    My CYA gradually disappears. My location in central Minnesota. Pool temp is kept between 83F and 87F. Whenever we are not in the pool, the safety cover is on, so the pool gets relatively no sunlight. To counter act the CYA disappearance, I periodically add dichlor or trichlor instead of liquid bleach. Any idea what is happening here? This past week the chlorine suddenly went to zero and the water got slightly cloudy, so I added a lot of liquid bleach. Today (Aug 5), I noticed that the CYA is suddenly lower. Hmmm....

    Here is a complete history of this year's chem numbers and the chems added:

    City Water tested on 2011 05/28
    FC 1
    pH 7.8
    T/A 120
    CH 130
    Temp 48F

    2011 05/17 Open pool and start pump
    FC 0
    CC 0
    TC 0
    pH 7.5
    T/A 130
    CH 60
    CYA 0
    Temp 48F
    Borates 15ppm

    2011 05/18
    FC 3
    CC 25
    TC 28
    pH 7.2
    T/A 130

    2011 05/19
    FC 2
    CC 19
    TC 21
    pH 7.2
    T/A 130
    CH 70
    CYA 30
    Temp 49F

    2011 05/21
    FC 1
    CC 12
    TC 13
    pH 7.0

    2011 05/22
    FC 1
    CC 7
    TC 8
    pH 7.0

    2011 05/23
    FC 7
    CC 1
    TC 8
    pH 7.0
    Temp 54F

    2011 05/24
    FC 8
    CC 1
    TC 9
    pH 7.2
    Temp 54F

    2011 05/25
    pH 7.3

    2011 05/26 1
    FC 12
    CC 1
    TC 13
    pH 7.4
    Temp 54F

    2011 05/26 2
    FC 16
    CC 1
    TC 17
    pH 7.4
    T/A 120
    CH 70
    CYA 35
    Temp 56F

    2011 06/02
    FC 5.5
    CC 2
    TC 7.5
    pH 7.7
    T/A 100
    CH 70
    CYA 30
    Temp 81F

    2011 06/05
    FC 2.5
    CC 0.5
    TC 3
    pH 7.5
    Temp 89F

    2011 06/07
    FC 6
    CC 1
    TC 7
    pH 7.6
    Temp 87F

    2011 06/09
    TC 2
    pH 7.8
    Temp 82F

    2011 06/11
    FC 7
    CC 0.5
    TC 7.5
    pH 7.8
    Temp 78F

    2011 06/18
    FC 7.5
    CC 0.5
    TC 8
    pH 7.8
    Temp 87F

    2011 06/25
    FC 2
    CC 0.5
    TC 2.5
    pH 7.8
    T/A 100
    CH 70
    CYA 33
    Temp 87F

    2011 07/02
    FC 1.5
    CC 0.5
    TC 2
    pH 7.7
    Temp 88F

    2011 07/03
    FC 6
    CC 0.5
    TC 6.5
    pH 7.6
    Temp 88F

    2011 07/05
    FC 0
    pH 7.8
    Temp 84F

    2011 07/06
    FC 23
    CC 0.5
    TC 23.5
    pH 8.2
    Temp 83F

    2011 07/07
    FC 19.5
    CC 0.5
    TC 20
    pH 8.2
    Temp 83F

    2011 07/08
    FC 14
    CC 0.5
    TC 14.5
    pH 7.4
    T/A 90
    CH 70
    CYA 30
    Temp 82F

    2011 07/09
    FC 9
    CC 0.5
    TC 9.5
    pH 7.4
    T/A 90
    CH 80
    CYA 25
    Temp 86F

    2011 07/10
    FC 7
    CC 0.5
    TC 7.5
    pH 7.4
    Temp 85F

    2011 07/13
    FC 12
    CC 0.5
    TC 12.5
    pH 7.4
    Temp 82F

    2011 07/16
    FC 10
    CC 0.5
    TC 10.5
    pH 7.5
    Temp 78F

    2011 07/22
    FC 12
    CC 0
    TC 12
    pH 7.4
    T/A 90
    CH 80
    CYA 20
    Temp 88F

    2011 07/25
    FC 8
    CC 0.5
    TC 8.5
    pH 7.5
    Temp 86F

    2011 07/29
    FC 8
    CC 0.5
    TC 8.5
    pH 7.5
    T/A 80
    CH 70
    CYA 30
    Temp 87F

    2011 07/31
    FC 6.5
    CC 0.5
    TC 7.0
    pH 7.4
    T/A 80
    CH 70
    CYA 30
    Temp 86F

    2011 08/02 1
    FC 0
    pH 7.2
    Temp 83F

    2011 08/02 2
    FC 13.5
    CC 1.0
    TC 14.5
    pH 7.3
    Temp 84F

    2011 08/03
    FC 17.5
    CC 1.0
    TC 18.5
    pH 7.4
    Temp 83F

    2011 08/04
    FC 13.0
    CC 0.5
    TC 13.5
    pH 7.5
    Temp 83F

    2011 08/05
    FC 8.0
    CC 0.5
    TC 8.5
    pH 7.5
    T/A 100
    CH 70
    CYA 10
    Temp 82F
    Borates 20ppm

    Chemicals added and the expected result based on TFP calculator iPhone app:
    Pool startup
    2011 05/17
    84oz dichlor FC 20.2
    CYA 18 pH down .77
    4 jugs 12.5% chlorine FC 28.8
    2 boxes Borax pH up .35

    2011 05/18
    32oz dichlor FC 7.7
    CYA 7 pH down .29
    2 jugs 12.5% chlorine FC 14.4
    2 boxes Borax pH up .35

    2011 05/19
    4 jugs 12.5% chlorine FC 28.8

    2011 05/20
    2 jugs 12.5% chlorine FC 14.4

    2011 05/21
    2 jugs 12.5% chlorine FC 14.4

    2011 05/22
    4 jugs 12.5% chlorine FC 28.8

    2011 05/23
    1 jugs 12.5% chlorine FC 7.2

    2011 05/24
    1 jugs 12.5% chlorine FC 7.2

    2011 05/26
    20oz dichlor FC 4.8
    CYA 4 pH down .18

    2011 06/01
    1 jugs 12.5% chlorine FC 7.2

    2011 06/02
    32oz dichlor FC 7.7
    CYA 7 pH down .29

    2011 06/05
    1 jugs 12.5% chlorine FC 7.2

    2011 06/08
    16oz dichlor FC 3.8
    CYA 3 pH down .15

    2011 06/15
    1 jugs 12.5% chlorine FC 7.2

    2011 06/25
    1 tablet 7oz trichlor FC 2.8
    CYA 2 pH down .15

    2011 06/27
    1 tablet 7oz trichlor FC 2.8
    CYA 2 pH down .15

    2011 07/02
    1 jugs 12.5% chlorine FC 7.2

    2011 07/05
    3 jugs 12.5% chlorine FC 21.6

    2011 07/07
    2 quarts 31.45% 20 baume muriatic acid pH 0.7 down

    2011 07/10
    3 lbs baking soda pH up 0.4
    3 tablets 7oz trichlor FC 8.3
    CYA 5 pH down .45

    2011 07/16
    2 tablets 7oz trichlor FC 5.6
    CYA 3 pH down .30

    2011 07/24
    1 tablet 7oz trichlor FC 2.8
    CYA 2 pH down .15

    2011 07/28
    1 tablet 7oz trichlor FC 2.8
    CYA 2 pH down .15

    2011 07/31
    3 lbs baking soda pH up 0.4
    1 jugs 12.5% chlorine FC 7.2

    2011 08/02
    3 jugs 12.5% chlorine FC 21.6
    1 jugs 12.5% chlorine FC 7.2
    18' X 36' X 4.5' vinyl oval in-ground 17K gallons, 250K BTU Pentair Master Temp NG heater, 1HP Hayward Super Pump, Hayward S200 sand filter, Hayward Pool Vac, Extreme mesh safety cover, TF-100 test kit.

  2. Back To Top    #2
    dmanb2b's Avatar
    Join Date
    Apr 2009
    Location
    NY
    Posts
    3,728

    Re: CYA disappears

    Hi, sorry to here about your troubles. What test kit are you using to measure CYA down to 2ppm? The K2006 or TF100 at best can only measure down to 20ppm, anything lower should be considered zero. That said, any chance you have an autofill device that may be masking a leak? How long does the pool stay covered for?

    We have heard of cases where CYA converts to ammonia over the winter, but odd to see that happen during the swim season
    24'x52" AGP (13,500 Gallons), Intex SWG, (2)Solar Bear 4x20 panels, Hayward S220T Filter, 1/2hp Pentair Superflo

    Pool School, TFTestKits, Pool Calculator

  3. Back To Top    #3

    Join Date
    Apr 2009
    Location
    Central Minnesota
    Posts
    74

    Re: CYA disappears

    I am using the TF-100 test kit.
    I think you read my post wrong. The 1st half of the post is my actual measurements. The 2nd half of the post is the chemicals I added and their expected change to my pool chemistry based on the TFP iPhone Pool calculator app.

    No autofill device. Actually we have had so much rain this summer, that I seldom have had to add water. Since the pool opening and initial top off, I probably have only added 6 inches of city water total this summer.

    The pool probably gets used every 3rd day, where the cover will be off for 3 hours. So say, maybe it gets exposed to the sun 8-10 hours a week. The rest of the time it is covered with an extreme safety cover that lets very little light through it.
    18' X 36' X 4.5' vinyl oval in-ground 17K gallons, 250K BTU Pentair Master Temp NG heater, 1HP Hayward Super Pump, Hayward S200 sand filter, Hayward Pool Vac, Extreme mesh safety cover, TF-100 test kit.

  4. Back To Top    #4

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: CYA disappears

    High chlorine levels can slowly oxidize CYA. Usually though, normal chlorine levels would lower CYA at a rate of around 2-3 ppm per month. In a hot spa we typically see around 5 ppm CYA per month drop. It's possible something in the water is catalyzing the reaction to go faster or there could be some water leak/refill going on (you can do a bucket Leak Detection test to verify that).
    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"

  5. Back To Top    #5

    Re: CYA disappears

    Has the rain been enough to make the pool overflow? or to make you have to lower the water level on purpose?
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

  6. Back To Top    #6

    Join Date
    Apr 2009
    Location
    Central Minnesota
    Posts
    74

    Re: CYA disappears

    This is a followup to an old post that I started back in 2011. I still have significant CYA loss over the winter. Not that it really matters as I simply use trichlor and dichlor until the CYA is up, then I switch to liquid chlorine. I am just curious as to what is happening. This spring 2016 CYA was 0. I use the TF-100 test kit. In Minnesota our season is short. Typically open Memorial weekend and close week after labor day.

    Here are my results from 2011 - 2016 when doing an initial water test when opening pool in the spring. Pump is running for about an hour when I take the measurement. I close the pool with a shock FC of about 15-20.

    2011 05/17
    FC 0
    CC 0
    TC 0
    pH 7.5
    T/A 130
    CH 60
    CYA 0
    Temp 48F
    Borates 15ppm

    2011 ended with CYA 45
    Note: Replaced liner. New water fill. Obviously no CYA
    2012 06/04
    FC 0.0
    CC 0.0
    TC 0.0
    pH 8.2
    T/A 160
    CH 90
    CYA 0
    Temp 87F

    2012 ended with CYA 50
    2013 05/14
    FC 0.0
    CC 0.0
    TC 0.0
    pH 7.0
    T/A 90
    CH 90
    CYA 35
    Temp 44F

    2013 ended with CYA 45
    2014 05/23
    FC 0.0
    CC 0.0
    TC 0.0
    pH 6.8
    T/A 70
    CH 70
    CYA 35
    Temp 51F

    2014 ended with CYA 60
    2015 06/09
    FC 14.5
    CC 0.5
    TC 15.0
    pH 6.9
    T/A 70
    CH 70
    CYA 20
    Temp 53F

    2015 ended with CYA 40
    2016 05/27 21:00
    FC 0.0
    CC 0.0
    TC 0.0
    pH 6.8
    TA 70
    CH 50
    CYA 0
    Temp 52F
    18' X 36' X 4.5' vinyl oval in-ground 17K gallons, 250K BTU Pentair Master Temp NG heater, 1HP Hayward Super Pump, Hayward S200 sand filter, Hayward Pool Vac, Extreme mesh safety cover, TF-100 test kit.

  7. Back To Top    #7
    bobodaclown's Avatar
    Join Date
    Apr 2011
    Location
    Lakeland, FL
    Posts
    2,351

    Re: CYA disappears

    I think you're experiencing is due to splash out and such. It's doesn't seem too out of line.
    17K Kidney Shaped Pool Concrete (Diamond Bright) Pool, 3/4 hp 2 speed 115V Sta-rite Duraglas PEA5D-180L/P2R5D-181L (Impeller C105-92PS Diffuser C1-216P), 1.5 piping, Pentair CC100 Filter , Heat Siphon 100K BTU Heat Pump Pool Heater, Flow meter Blue White Flowmeter Model No. F-30150P, Hayward Astrolight SP0581N, SWCG CalimarTitanium Edition TE45 , Dolphin Nautilus Plus with CleverClean, Lakeland Florida

  8. Back To Top    #8

    Join Date
    Apr 2009
    Location
    Central Minnesota
    Posts
    74

    Re: CYA disappears

    Zero CYA in the spring? Can't be splash out.
    18' X 36' X 4.5' vinyl oval in-ground 17K gallons, 250K BTU Pentair Master Temp NG heater, 1HP Hayward Super Pump, Hayward S200 sand filter, Hayward Pool Vac, Extreme mesh safety cover, TF-100 test kit.

  9. Back To Top    #9
    Mod Squad pooldv's Avatar
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    DFW, TX
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    23,994

    Re: CYA disappears

    I agree that CYA drops over time, more over winter usually. Mine does too and we don't close.
    TFP Moderator
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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

  10. Back To Top    #10

    Join Date
    Jun 2007
    Location
    Poughquag, NY
    Posts
    217

    Re: CYA disappears

    I'm in NY, use a mesh trampoline style cover when closing, so we get a lot of fine silt in the pool during the offseason. Open to a zero CYA pool every year for the last 10 years. Maybe it's the soil bacteria. We also drain down about 18 inches when closing, that gets replaced by snow and rain, so some dilution for sure. Part of my opening is to add CYA directly or sometimes with dichlor until the SWG is set to go. Once I'm at 60 to 80 ppm, I'm generally good for the season.
    20 x 40 vinyl IG. SWG. Solar. Ikeric VS pump.

  11. Back To Top    #11
    mikemass's Avatar
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    Jul 2013
    Location
    Northern Howell, NJ
    Posts
    484

    Re: CYA disappears

    OP - There's an current thread ongoing where a member posted the same problem. Then one of the senior TFP guys chimed in on how bacteria turning to ammonia can eat up CYA over the winter. I have owned 2 pools over the course of about 27 years now and this is the answer I was finally looking for. I would like to read some more scientific evidence on this. But so far this explanation makes a lot of sense to me. Read about it here:

    Opened pool, CYA has gone
    25 + year pool owner. Current pool (going on 11th year) - 38K gallon in ground Gunite/White Plaster, Spillover Spa, Hayward Cartridge Filter, Hayward 450k BTU NG Heater, Hayward Goldline Aqua Logic control with T-Cell-15 Salt Water Cell, Dolphin Explorer.
    You Need: Bleach, a A Test Kit & a Bookmark to "Pool School". Now what's your question?

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