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Thread: What is eating up my chlorine?

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    Unhappy What is eating up my chlorine?

    Hello, I have a 15k gallon in ground pebble tec pool with AutoPilot SWG, Polaris cleaner, and Sta Rite filter system. Over the last month or so, I've been having problems keeping up my chlorine levels without adding additional chlorine manually. I cleaned the salt cell which helped a little, but still can't keep chlorine. I am attempting to SLAM the pool now. I superchlorinated to 24ppm last night and was down to 18ppm this morning (lost 6ppm overnight). Before I added the chlorine, I sprayed off the filter cartridges. I don't have any visible algae although I did have a small amount of yellow algae and the pink algae/bacteria stuff earlier in the season. My CYA level is at 50ppm. A test for ammonia showed 0.5ppm. What are some other causes of chlorine loss? Should I just continue the SLAM until I'm not losing chlorine over night?

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    Mod Squad woodyp's Avatar
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    Re: What is eating up my chlorine?

    Welcome to the forum. Yes, continue to SLAM per Pool School and when finished, maintain your level of FC in relationship to your CYA level. Are you using one of our recommended test kits?
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    Re: What is eating up my chlorine?

    What FC do you normally maintain in the pool?
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
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    Re: What is eating up my chlorine?

    What are some other causes of chlorine loss?
    An important principle to remember for TFPC. Two things consume chlorine from your pool.....organics in the water and UV rays striking the water from the sun. That's it. The solution is ALWAYS more chlorine
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    What is eating up my chlorine?

    Outside of UV light, organics and biological sources, the only other sources of chlorine degradation would be oddball chemicals like ammonia, peroxide, ascorbic acid and certain sulfur compounds like sodium thiosulfate. None of those should be regularly going into the pool water.

    You did mention a 0.5ppm ammonia concentration. How was that measured?

    Another question is how are you "Superchlorinating" your pool? For a SLAM you should only be using liquid chlorine products (store bought bleach or higher concentration sodium hypochlorite from a hardware or pool store). SWGs all claim they can "Boost" or "Superchlorinate" but they can't typically generate the FC levels needed for a SLAM.

    Please provide test results (preferably from a Taylor K-2006 test kit) so we can help you further.

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    Re: What is eating up my chlorine?

    For chlorine, I'm using Taylor K-1515-A. For ammonia, I'm using the API ammonia test kit. I normally maintain FC of 3.

    When "superchlorinating", I'm using 8.5% bleach.

    I'll provide test results asap.
    Last edited by Butterfly; 09-18-2014 at 01:28 PM. Reason: Removed link.

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    What is eating up my chlorine?

    Assuming you have no continuous source of ammonia, the shock FC levels will "burn it off" (convert it into CCs). It takes time but it should go away. If you continue to measure ammonia, then you'll need to see if that's just bather waste or some other source.

    If you get a K-2006 kit, then you'll have everything in the 1515-A plus all the other tests as well.

    And, the most important question of course is this - what is your CYA level? That's the most important place to start.



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    Mod Squad tim5055's Avatar
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    Re: What is eating up my chlorine?

    Quote Originally Posted by jkalin1 View Post
    I normally maintain FC of 3.

    When "superchlorinating", I'm using 8.5% bleach.

    I'll provide test results asap.
    that explains your algae. For CYA 50 you have listed the Minimum you FC should ever be is 4. You want to target 6 - 8 to cover loss to UV during the day. The 3 has just been holding off a full algae bloom and making your SWG work harder and harder.

    With a SWCG we recommend CYA 70 - 80, but don't raise it until the SLAM is over and you are sure all the algae is dead.

    Read through the directions for a SLAM as you need to follow them all the way to the end
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: What is eating up my chlorine?

    @tim5055

    Nailed it!!

    I missed the CYA 50ppm part.




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    Re: What is eating up my chlorine?

    Tim caught why I was asking. Although 3-4 is the minimum for a salt pool, I recommend a target of 5-6, because there are times where the FC will be consumed faster than others, and you want to make sure you never fall under 3.
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
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    Re: What is eating up my chlorine?

    Thanks for all the great feedback so far! I'll aim for a FC of 5-6 once I get through this. Always heard 5 was too high to swim.

    Latest numbers:
    FC 21 (last evening 11pm)
    FC 20 (this morning 7am)
    CC 0
    Ammonia 0
    CYA 60 (after testing again, looks closer to 60 than 50)
    Hardness 250
    Alk 110
    PH 7.6

    I'll do another overnight test tonight, but only lost 1ppm over night so hoping I'm good to go.

    Question - is it ok/recommended/not recommended to run the SWG while SLAMing? I don't have the ability to add more chlorine during the day while I'm at work.

    Also, I still haven't seen any algae - is it possible algae may be in the plumbing?

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    What is eating up my chlorine?

    You can run your SWG during the SLAM. However, if you do an OCLT, it has to be shut off and all of your pumps need to be running overnight in order to be a valid OCLT.



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    Mod Squad JVTrain's Avatar
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    Re: What is eating up my chlorine?

    Quote Originally Posted by jkalin1 View Post
    Thanks for all the great feedback so far! I'll aim for a FC of 5-6 once I get through this. Always heard 5 was too high to swim.

    Latest numbers:
    FC 21 (last evening 11pm)
    FC 20 (this morning 7am)
    CC 0
    Ammonia 0
    CYA 60 (after testing again, looks closer to 60 than 50)
    Hardness 250
    Alk 110
    PH 7.6

    Also, I still haven't seen any algae - is it possible algae may be in the plumbing?
    There is no constant maximum FC level where it is safe to swim for all pools. Well there is, but it depends on your CYA level. If you go to the Chlorine/CYA chart the shock level for each specific CYA concentration is the level up to where it's safe to swim. For instance, at your 60 CYA it would be safe to swim at up to 24 ppm FC.

    If you don't see algae, that's great. You might have algae in your filter but it will all be dead by the end of the SLAM. You'll then backwash it out or clean it off your filter. Speaking of that... you should add the details of your pool to your forum signature as well as update your location. Location does matter when giving advice.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
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    Mod Squad tim5055's Avatar
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    Re: What is eating up my chlorine?

    Quote Originally Posted by jkalin1 View Post
    Always heard 5 was too high to swim.
    yup, that is what the pool stores will tell you. They don't understand or don't care about the relationship between FC and CYA. But, I guess if you get an algae bloom that gives them the opportunity to sell you algaecide, floculant and any number of magic potions to solve your problems.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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