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Thread: Pool opening issue - cannot hold free chlorine

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    Pool opening issue - cannot hold free chlorine

    Hello TFP Forum! I've been following the forum for about a year, and this is my first post.

    We opened the pool two days ago to cloudy water, and testing with TFT-100 produced the following:

    free chlorine: 0
    combined chlorine: 0
    CYA: 0
    pH: 7.2
    CA:150 ppm
    Alkalinity:80 ppm

    Saturday I added 6 lb of stabilizer followed by 3 lb cal-hypo. Tested for chlorine a few hours later, and no free or combined chlorine was detected.

    Yesterday I added 4 gal of 12.5% liquid chlorine and tested 2 hrs later - free chlorine: 1ppm; combined chlorine: 7 ppm.

    I tested again early this morning, and all free and combined chlorine was gone,

    I then added 4 more gal of 12.5% chlorine and tested 2 hr later - free c: <1; combined c: 7ppm.

    should I continue this pattern or change my approach?
    pool info: in-ground, 18' x 36', 26000 gal, vinyl liner
    62GPM sand filter, 3/4 HP pump

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    njboater74's Avatar
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    Re: Pool opening issue - cannot hold free chlorine

    You're CYA being at 0 is an issue. What did you use as the stabilizer? Was it liquid or powder? You'll want to get the CYA up to 30 ppm otherwise you'll lose your FC to the sun. It was hot weekend here in NJ.

    The combined chlorine suggests that the chlorine is working on the pool, so you have the combination of sunlight and substances eating up your chorine. Is your water getting clearer?

    1. Get the CYA up to 30.
    2. Start the SLAM method
    3. You know you're done when your FC holds overnight, and your CC is less than 1.
    33k gallon, 40x20 IG Vinyl, Hayward sand filter, Hayward pump
    Hayward multiport valve, TF-100 Test Kit.

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    Re: Pool opening issue - cannot hold free chlorine

    Already added another 2 lb stabilizer (granular). That should get me to around 30 ppm.
    I have yet to get to 10 -12 ppm free chlorine. is there any limit to the quantity of chlorine that can be added at one time?
    pool info: in-ground, 18' x 36', 26000 gal, vinyl liner
    62GPM sand filter, 3/4 HP pump

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    AimeeH's Avatar
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    Re: Pool opening issue - cannot hold free chlorine

    Quote Originally Posted by Oldguy View Post
    Hello TFP Forum! I've been following the forum for about a year, and this is my first post.

    We opened the pool two days ago to cloudy water, and testing with TFT-100 produced the following:

    free chlorine: 0
    combined chlorine: 0
    CYA: 0
    pH: 7.2
    CA:150 ppm
    Alkalinity:80 ppm

    Saturday I added 6 lb of stabilizer followed by 3 lb cal-hypo. Tested for chlorine a few hours later, and no free or combined chlorine was detected.

    Yesterday I added 4 gal of 12.5% liquid chlorine and tested 2 hrs later - free chlorine: 1ppm; combined chlorine: 7 ppm.

    I tested again early this morning, and all free and combined chlorine was gone,

    I then added 4 more gal of 12.5% chlorine and tested 2 hr later - free c: <1; combined c: 7ppm.

    should I continue this pattern or change my approach?
    Hi, welcome to TFP

    Im thinking that 7cc with <1ppm chlorine is a typo?

    With cloudy water upon opening, I'd suspect you've got some algae which is quickly consuming your chlorine. You've added CYA, did you use pool math to get to a target? It can take a while for all the granule CYA to dissolve but once it does it should show up on a test. I would assume your CYA is at target and raise your free chlorine to SLAM level.

    Have you read up on defeating algae in pool school? It references the SLAM procedure to get rid algae. Pool School - Defeating Algae

    You need to keep FC at SLAM level for your CYA until you pass all three tests

    Clear water
    Cc<.5
    Overnight free chlorine loss of <1
    18*36*23 true "L" vinyl IG 29,000 gallons. SWG. TF-100 test kit.
    http://tftestkits.net/splash-page.html

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    Mod Squad JVTrain's Avatar
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    Re: Pool opening issue - cannot hold free chlorine

    You should not have the FC any higher than the shock level recommended in the CYA/Chlorine chart. See link in my signature. Having the FC higher than that is "wasting" chlorine as the shock level at each CYA is enough to kill algae. Also, if you go above that level it's hard on your liner and pool equipment over time. Also would be harsh on anyone who jumped in, including their swimsuits. Going a few points over is not a disaster as chlorine is a consumable and will come down fairly quickly but it's not doing any more good than having it at the proper shock level for your CYA.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
    40x20 Pool: 32K Gallons * Vinyl * Bleach Chlorination * Hayward S270T Sand Filter * Pentair SuperFlo 1 HP * Teledyne/Laars Heater * AquaVac Tigershark * TF-100 w/ SpeedStir
    Isolated Spa - 345 Gallons

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    njboater74's Avatar
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    Re: Pool opening issue - cannot hold free chlorine

    Quote Originally Posted by Oldguy View Post
    Already added another 2 lb stabilizer (granular). That should get me to around 30 ppm.
    I have yet to get to 10 -12 ppm free chlorine. is there any limit to the quantity of chlorine that can be added at one time?
    You can add as much chlorine as you need at once, but as JVTrain mentioned, you don't want to exceed the total 12ppm of FC.

    Are you still using cal-hypo? You might want to consider using bleach/liquid chlorine instead. The cal-hypo adds calcium to your pool, which doesn't really make much of a difference with your vinyl liner. In my experience fighting algae, the bleach (since it doesn't need to disolve) seems to work faster and more reliably than granulated chlorine products.
    33k gallon, 40x20 IG Vinyl, Hayward sand filter, Hayward pump
    Hayward multiport valve, TF-100 Test Kit.

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    Re: Pool opening issue - cannot hold free chlorine

    I added another4 gal of 12.5% liquid chlorine again earlier this evening. My procedure is to add 2 gal, wait for 30 minutes and test. If free chlor value is nowhere near shock level ( 10 -12 ppm ), then add next 2 gal, wait 30 minutes and test for free & combined chlorines.

    results:
    free chlor: 2 ppm - combined chlor: 7 ppm

    I don't appear to be making any headway.

    I have performed this procedure 3 times over the last 2 days, and under normal circumstances, the free chlorine should have increased by 18 ppm. what I consistently get is 1 - 2 ppm free and around 7 ppm combined chlorine . Where is the rest going??
    pool info: in-ground, 18' x 36', 26000 gal, vinyl liner
    62GPM sand filter, 3/4 HP pump

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    njboater74's Avatar
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    Re: Pool opening issue - cannot hold free chlorine

    You're making headway. You wouldn't see the 7.0 ppm of CC if it wasn't doing anything. That means there's something in the water that the chlorine is trying to deal with. Algae will eat up FC very fast.

    Besides, 30 minutes may not be enough time to get a totally accurate reading, depending on your circulation. The chlorine needs to circulate around the pool. Furthermore, when you have an algae bloom, 2 gallons isn't going to be enough to get it up to 12. So by the time you've added the next 2 gallons, the FC level is back down again.

    Have you consulted the calculator here http://www.troublefreepool.com/calc.html

    This is saying you need 319 oz (2.5 gallons) of 12.5% to get up to shock level. You're getting it close, but the algae keeps eating the chlorine. You need to get it all the way up at once to attack the algae so that the chlorine can kill the algae faster than the algae can reproduce.

    I've been exactly where you are. Felt I wasn't making headway until I finally added enough to get up to shock level all at once. Then started seeing progress. Once you have started killing the algae, it will eat your FC less rapidly making it easier to maintain your shock level.

    You're making progress. Keep it up.

    - - - Updated - - -

    You may also want to consider going to Mustard Algae shock levels (which would actually be 18ppm), as outlined in this chart:
    Chlorine/CYA Chart

    Again, it's very important that you actually reach these levels when attacking algae. They're designed to kill algae faster than they reproduce. If your level is too low, the algae can keep reproducing.
    33k gallon, 40x20 IG Vinyl, Hayward sand filter, Hayward pump
    Hayward multiport valve, TF-100 Test Kit.

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    Swampwoman's Avatar
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    Re: Pool opening issue - cannot hold free chlorine

    Hi Oldguy.
    Your rate of chlorine consumption/not holding FC seems a little suspicious to me, but there could be a couple of things at work.

    If your FC still isn't holding and you've now had a day of the cya dissolving, can you first report back the results of a fresh cya reading -- you've now added 8 lbs cya, right? So you should read 37 ppm.

    Did you open the pool yourself, and did any RV antifreeze (pink stuff) get in the water...or was the filter set to waste on opening to clear it?

    What was your cya when you closed last year?

    Lastly, though RARE, there is a chance that if your FC & CYA sat together at 0 for very long, you could have developed ammonia that converted from your cya. Normally, that's more likely in swamp conditions with a long closing, but if that's the case you can either pick up a cheap ammonia test at a pet store, or do the following dosing test before adding any more cya:



    Ammonia Diagnosing:
    1. Test CYA level and record result
    2. With pump running, dose FC to Shock (SLAM) per level per Pool School - Chlorine / CYA Chart, then retest FC after 10 minutes. If FC level drops by more than 50%, then proceed with treatment for ammonia.

    Treatment for Ammonia:
    1. Begin a SLAM and dose FC up to SLAM level. Do not add additional CYA at this point.
    2. Retest FC at 10-minute intervals.
    a. If FC loss is greater than 50%, add FC to bring back up to SLAM level and continue retesting FC @ 10-minute intervals.
    b. IF FC loss is 50% or less, add FC to bring back up to SLAM level. Go to Step 3.
    3. If CYA is below 30 ppm, add enough CYA to bring level up to 30 ppm.
    4. Continue SLAM as directed in the SLAM article until the SLAM Criteria of Done are met. Test as directed in the SLAM article - no longer need to test FC at 10 minute increments at this point.
    In ground extended Grecian, 22,000 gal, Hayward 220t sand filter, vinyl liner, dolphin m4 supreme.
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    Helpful Links:
    GET A TEST KIT Chlorine/CYA Chart How to SLAM About Metals & Stains

  10. Back To Top    #10

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    Re: Pool opening issue - cannot hold free chlorine

    Well, after several days of repeated shocking with a mixture of 12.5% bleach, cal-hypo and non-chlorine MPS, the pool has finally cleared and passed the overnight free chlorine test.

    I don't believe I was fighting algae, but rather the organic compounds leftover from the degradation of CYA last winter while the pool was covered.
    pool info: in-ground, 18' x 36', 26000 gal, vinyl liner
    62GPM sand filter, 3/4 HP pump

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