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Thread: Pool will not hold free Chlorine level overnight

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    Pool will not hold free Chlorine level overnight

    Trying to open and balance the pool this year has become a nightmare. After repeated shocking ,the free chlorine level still dissipates overnight . latest readings are TC 2.1 FC 0 PH 8.4 Alkality 130 Calcium hardness 225 CYA 80 . (done by a well respected pool store). The water is clear with no visible signs of algae growth. To try and figure out the problem without spending hundreds more dollars in chemicals Iam now using a 5 gal test bucket. My latest attempt to try to reach breakpoint in the test is adding 1 oz of 8.25% bleach in 5 gal of pool water, which should be the equivalent (If my reasoning is correct) of adding 42 gal of the 8.25% solution to my 27,000 gal pool. To my way of thinking, this should raise the FC level well over the point necessary to kill off whatever is eating the chlorine . After adding the liquid chlorine to the test container , the test strip showed dark purple, but FC was gone overnight. Any suggestions would certainly be appreciated
    26,7000 gal I/G vinyl 1HP pump S220T sand filter inline chlorinator

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    mrcarcrazy's Avatar
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    Re: Pool will not hold free Chlorine level overnight

    Time and concentration are both keys in killing off algae IIRC. FWIW 42 gals at one time in a pool will yield an amazingly high FC number (~125 per pool math tab above). There is such thing as too much FC....

    everyone here will start by saying you really need a good test kit for yourself. (you will be testing it frequently if you follow the SLAM guidelines outlined in "pool school".) Not to mention it's great having the power to test it whenever you please and trust the results 100%.
    IG gunite/plaster pool/spa Started 1/17/14, Plastered 5/16/14
    Size: 12'-21'x39' free form, depth ranging from 4' to 7, attached 6 person spa with spillover.
    Equipment: Whisperflo 2hp pump, Pentair 30" sand filter, Pentair Mastertemp 400k BTU heater, 1hp Whisperflo for waterfalls, and a blower for spa floor

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    JesseWV's Avatar
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    Re: Pool will not hold free Chlorine level overnight

    Did you add CYA at opening? How much was there at closing?
    16k gal, 28'x3.5', Vinyl A/G, 1hp Pentair Dynamo 2-speed Pump, Hayward S160T Sand Filter, Intermatic HB800RCL Digital Timer, Intex 8110 SWG, TF-100 Test Kit, SpeedStir Author: Jesse's Graphical Pool Testing Log

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    Charlie_R's Avatar
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    Re: Pool will not hold free Chlorine level overnight

    Welcome to TFP!

    I will second what Mrcarcrazy said: You need your own test kit.

    Do yourself a favor, and click on the link in the upper right of every page here, and read Pool School. Pay particular attention to the test kit comparison, and defeating algae.

    You are gong to have to do what we call SLAM your pool. That is Shock Level And Maintain. Following the CYA/FC chart in Pool School, you need to bring your FC level up to the appropriate level, and KEEP IT THERE, until you are no longer losing FC overnight.

    I'm sure there are others here that will chime in with essentially the same info, and probably expand on it.

    You can take control of your pool, and not waste so much $$ on pool store chemicals.
    15'x48" 4500 gallon Intex pool, buried 1.5 ft. Pac-Fab Dynamo 3/4 hp pump. Hayward S180T sand filter, bought used. Taylor K-2006 test kit. Rocket mass heater based wood fired pool heater.

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    Re: Pool will not hold free Chlorine level overnight

    Need to bring the PH down into the acceptable range of 7.2-7.6
    210k gallon pool, IG Plaster, (2) marathon 7.5 hp motors, (6) Triton sand filters, Test Kit Guardex 4-in-1 Plus DPD & Taylor K-2006, Baby pool 6in deep round with stand alone sand filter.

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    JesseWV's Avatar
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    Re: Pool will not hold free Chlorine level overnight

    Quote Originally Posted by bbenjamin View Post
    Need to bring the PH down into the acceptable range of 7.2-7.6
    ^^ THIS! A pH reading of 8.4 could mean it's even higher since it's at the limit of the test. Either way, high pH reduces the effectiveness of chlorine.
    16k gal, 28'x3.5', Vinyl A/G, 1hp Pentair Dynamo 2-speed Pump, Hayward S160T Sand Filter, Intermatic HB800RCL Digital Timer, Intex 8110 SWG, TF-100 Test Kit, SpeedStir Author: Jesse's Graphical Pool Testing Log

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    Re: Pool will not hold free Chlorine level overnight

    Another test today (from another source) showed ph at 7.7 A little closer to the target
    26,7000 gal I/G vinyl 1HP pump S220T sand filter inline chlorinator

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    Re: Pool will not hold free Chlorine level overnight

    I think the component I've been missing is frequency. From what I'm hearing I should keep pounding it in increments of 8-12 hrs not to exceed 24 hours until the readings hold. I have been shocking then waiting a couple of days then shocking it again. I'm going to do the slam making sure I check and reshock 2-3 times per day min
    26,7000 gal I/G vinyl 1HP pump S220T sand filter inline chlorinator

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    Task's Avatar
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    Re: Pool will not hold free Chlorine level overnight

    CDA, frequency is definitely important. I'm a first year pool owner and I'm still just learning. I don't pretend to be one of the knowledgable people on this forum, but the key is really having your own test kit. The TF-100 is the way to go. I just finished SLAMing my pool about two weeks ago. It took me about a week to clear up the water and for the first few days, I needed to test my water hourly, or as close to hourly as I possibly could given my time schedule. You need accurate test results, especially your CYA levels so you know what FC level you need to maintain throughout the SLAM process. After 1 week, 15 gallons of 12.5% liquid chlorine, and lots of brushing, my pool was crystal clear and has remained that way as I have been testing chlorine and PH daily ever since and doing a complete round of testing once a week.
    16'x32' Inground Vinyl, 21,100 gallons, Hayward 1.5 HP Super Pump, Hayward Pro Series S244T 3.1ft Sand Filter
    TFTestKits, Pool School, ABC's of Pool Water Chemistry, Chlorine/CYA Chart, PoolMath

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    Beens's Avatar
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    Re: Pool will not hold free Chlorine level overnight

    What task said!

    18' x 48" (42" water depth) Intex Metal Frame 6,700 Gallons
    Hayward Power-Flo LX 1.0 HP pump
    Hayward Pro Series S166T Sand Filter
    Original Intex Floating Skimmer

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