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Thread: I can't keep my free chlorine level up!

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    I can't keep my free chlorine level up!

    I added ascorbic acid to my fiberglass pool a couple of weeks ago and got rid of all my stains but can't seem to get my free chlorine level up! I thought I had a handle on it with bleach and raising my chlorinator to 100% but I came back from being gone for the weekend and my level is back down to 0. But my Total Chlorine is at 3! I'm so confused. I don't even know the difference between the two!!
    Templehb - 16,000 gal fiberglass inground pool, Aquapure 1400 SWG, DE filter.

  2. Back To Top    #2
    whoozer's Avatar
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    Copied and pasted per sticky (what to test for and what it means):

    FC - Free Chlorine

    Free chlorine shows the level of disinfecting chlorine available to keep your pool sanitary. FC should be tested and chlorine added daily, unless you have an automatic feeder or SWG in which case you can test it every couple of days. FC is consumed by sunlight and when it breaks down organic material in your pool. The level of FC you need to maintain depends on your CYA level and how much your pool is used. See The Pool Calculator, Chlorine/CYA Chart by Chemgeek, or Ben's Best Guess Chart for guidelines on the appropriate FC level to maintain based on your CYA level. It is important that you do not allow FC to get too low or you run the risk of getting algae and/or having an unsafe pool.

    FC is raised with bleach, trichlor tablets/pucks/sticks, dichlor powder, cal-hypo powder/capsules, or lithium hypochlorite. Only use bleach without any additives, typically labeled unscented or "original scent". Trichlor and dichlor also add CYA and lower PH. Cal-hypo also adds calcium. Lithium hypochlorite tends to be quite expensive. It is most efficient to raise the FC level in the evening since none will be lost to sunlight until the next morning. FC normally goes down by itself. If you are in a hurry you can lower FC with a chlorine neutralizer.

    CC - Combined Chlorine

    Combined chlorine is an intermediate breakdown product that is created in the process of sanitizing the pool. CC causes the "chlorine" smell some people associate with chlorine pools. If CC is above 0.5 you should shock your pool. CC indicates that there is something in the water that the FC is in the process of breaking down. CC will normally stay at or near zero as long as you maintain an appropriate FC level and the pool gets some direct sunlight.

    Potassium monopersulfate (a common non-chlorine shock) will often show up on tests as CC. There is a special reagent you can get to neutralize the potassium monopersulfate so you can get a true CC reading.

    TC - Total Chlorine

    Total chlorine is the sum of FC plus CC. Inexpensive chlorine tests, such as the common OTO test which shows TC as different shades of yellow, normally show TC because it is easier to test for than FC and CC. In normal operation TC can be used as if it was FC because CC is usually zero. However when you have algae or some other problems, CC levels can be significant and TC becomes useless.
    14x33 fiberglass freeform
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    AnnaK's Avatar
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    The best article I ever read about the various ingredients of the BBB method and their relationship to each other is in the TFP May 2008 Newsletter. I would strongly urge you to take a look at that, it'll answer several of your questions.

    What method do you use to test the water? If you use strips your measurements are not likely to be very accurate. We recommend that you purchase a good test kit. I prefer the TF-100, available here.

    Would you please post a full set of test results? There are a number of factors which influence free available chlorine, combined chlorine, and total chlorine.

    What do you put in the chlorinator? How long do you run the pump? Indoor or outdoor pool? What sun exposure do you have?

    We can surely help you but we need your test numbers and some pool specifics to do that.
    — AnnaK —

    12,000 gal AGP, Hayward sand filter, Pentair 2-speed pump, timer.
    Please visit our Pool Issues pages for information about step weights, managing the solar cover, and PoolSkim.

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    JasonLion's Avatar
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    You need to shock the pool. Any time CC is above 0.5 you should raise FC to shock level and hold it there till CC goes to zero. You said FC is 0 and TC is 3 and that means that CC is 3, well above 0.5. However, if you do that you risk bringing the stains back.

    The trick is to balance things, to add more and more chlorine, but not so much that the stains come back.

    If you post a full set of test results and the size of your pool, we can give you some more specific advice.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  5. Back To Top    #5

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    Ok, let's see if I can give you all the info you need (I'm still new at this). I have a 16,000 gallon in ground fiberglass pool. We have a salt system and chlorinator running about 3 hours a day at 100% right now. This is usually plenty of time to keep my chlorine at level. We live in the desert in southern California so we average 360 days of sun a year! My PH is at 7.2 and my alkalinity is 120. I test with a (and I'm reading this off the kit box) Taylor Service Complete (high) that tests chlorine, Bromine, PH with Acid & Base Demand, total alkalinity, Calcium Hardness, and Cyanuric Acid. Is this enough info???
    Templehb - 16,000 gal fiberglass inground pool, Aquapure 1400 SWG, DE filter.

  6. Back To Top    #6
    JasonLion's Avatar
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    It would be particularly good to know your CYA level.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  7. Back To Top    #7
    AnnaK's Avatar
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    Almost

    What's the CYA (cyanuric acid) reading?

    Your pH is too low. You should raise that to 7.6. According to the pool calculator (see link in Jason's sig line) you would add 33 oz of washing soda or soda ash, or 66 oz of borax (20 Mule Team in the laundry aisle).
    — AnnaK —

    12,000 gal AGP, Hayward sand filter, Pentair 2-speed pump, timer.
    Please visit our Pool Issues pages for information about step weights, managing the solar cover, and PoolSkim.

  8. Back To Top    #8
    JasonLion's Avatar
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    AnnaK, It is not a good idea to raise the PH much at all this soon after an ascorbic acid treatment, particularly when high chlorine levels are expected to follow shortly. After an ascorbic acid treatment you need to raise chlorine and PH levels gently and not at the same time, while monitoring for stains and adding more sequestrant as required.

    Even without the ascorbic acid treatment I would delay raising the PH because shocking is more effective at lower PH levels. Plus there is no need to change the PH just for the sake of hitting the target exactly. Anything from 7.2 to 7.8 is acceptable, and if it is in that range and not headed quickly out of that range there is no need to intervene.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  9. Back To Top    #9
    AnnaK's Avatar
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    Thank you Jason. I didn't know.
    — AnnaK —

    12,000 gal AGP, Hayward sand filter, Pentair 2-speed pump, timer.
    Please visit our Pool Issues pages for information about step weights, managing the solar cover, and PoolSkim.

  10. Back To Top    #10

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    Unfortunately, my kit is not registering a CYA level. When I put the solution in the tube, I'm supposed to wait for the black dot at the bottom of the tube to disappear and it never does! I am going to have my water tested at Leslie's but can't get there until Thursday.
    Templehb - 16,000 gal fiberglass inground pool, Aquapure 1400 SWG, DE filter.

  11. Back To Top    #11
    JasonLion's Avatar
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    That means your CYA level is near zero. When CYA is low it gets very difficult to maintain a FC level as sunlight will wipe out all your chlorine.
    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

  12. Back To Top    #12

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    Wow, you guys are awesome. I had no idea that's why that test was acting so funny. Now I just have to wait to go to the pool store on Thursday to buy cyanuric acid. I'm guessing the don't sell it anywhere but a pool store. (I live in the desert, closest pool store is 45 mins away, therefore I usually order on line.)
    Templehb - 16,000 gal fiberglass inground pool, Aquapure 1400 SWG, DE filter.

  13. Back To Top    #13
    frustratedpoolmom's Avatar
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    Sometimes you can find it at hardware stores or Wally World, it's also called "stabalizer".... or UV sunscreen I've even seen it called.
    Helpful links: Pool School; CYA/Chlorine Chart
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  14. Back To Top    #14

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    LOL, I guess I can throw some Coppertone in the pool so my FC won't get sunburned :P
    36,000 gallon IG Gunite (40 x 20), 1.5 HP Hayward pump, Pentair Nautilus NS-48 DE filter, 2 skimmers, 12 - (2 x 20) Fafco Solar Panels (Goldline controller not hooked up yet), Hayward Swimpure Plus SWG, Blue Pearl Robot cleaner. New Dr. Wellness X-12 standalone Lifestyle Spa.

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